mirror of
https://github.com/krahets/hello-algo.git
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Add Python codes for the chapter
of array and linked list.
This commit is contained in:
krahets
parent
9a861140d8
commit
cbf4ab0aaa
8 changed files with 503 additions and 22 deletions
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@ -20,12 +20,12 @@ class MyList {
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nums = new int[initialCapacity];
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}
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/* 获取列表容量 */
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/* 获取列表长度（即当前元素数量）*/
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public int size() {
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return size;
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}
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/* 获取列表长度（即当前元素数量） */
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/* 获取列表容量 */
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public int capacity() {
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return nums.length;
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}
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89
codes/python/chapter_array_and_linkedlist/array.py
Normal file
89
codes/python/chapter_array_and_linkedlist/array.py
Normal file
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@ -0,0 +1,89 @@
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'''
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File: array.py
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Created Time: 2022-11-25
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Author: Krahets (krahets@163.com)
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'''
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import sys, os.path as osp
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sys.path.append(osp.dirname(osp.dirname(osp.abspath(__file__))))
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from include import *
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""" 随机访问元素 """
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def randomAccess(nums):
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# 在区间 [0, len(nums)) 中随机抽取一个数字
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random_index = random.randint(0, len(nums))
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# 获取并返回随机元素
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random_num = nums[random_index]
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return random_num
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""" 扩展数组长度 """
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def extend(nums, enlarge):
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# 初始化一个扩展长度后的数组
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res = [0] * (len(nums) + enlarge)
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# 将原数组中的所有元素复制到新数组
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for i in range(len(nums)):
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res[i] = nums[i]
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# 返回扩展后的新数组
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return res
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""" 在数组的索引 index 处插入元素 num """
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def insert(nums, num, index):
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# 把索引 index 以及之后的所有元素向后移动一位
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for i in range(len(nums) - 1, index - 1, -1):
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nums[i] = nums[i - 1]
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# 将 num 赋给 index 处元素
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nums[index] = num
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""" 删除索引 index 处元素 """
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def remove(nums, index):
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# 把索引 index 之后的所有元素向前移动一位
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for i in range(index, len(nums) - 1):
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nums[i] = nums[i + 1]
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""" 遍历数组 """
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def traverse(nums):
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count = 0
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# 通过索引遍历数组
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for i in range(len(nums)):
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count += 1
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# 直接遍历数组
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for num in nums:
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count += 1
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""" 在数组中查找指定元素 """
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def find(nums, target):
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for i in range(len(nums)):
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if nums[i] == target:
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return i
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return -1
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""" Driver Code """
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if __name__ == "__main__":
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""" 初始化数组 """
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arr = [0] * 5
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print("数组 arr =", arr)
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nums = [1, 3, 2, 5, 4]
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print("数组 nums =", nums)
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""" 随机访问 """
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random_num = randomAccess(nums)
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print("在 nums 中获取随机元素", random_num)
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""" 长度扩展 """
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nums = extend(nums, 3)
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print("将数组长度扩展至 8 ，得到 nums =", nums)
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""" 插入元素 """
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insert(nums, 6, 3)
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print("在索引 3 处插入数字 6 ，得到 nums =", nums)
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""" 删除元素 """
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remove(nums, 2)
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print("删除索引 2 处的元素，得到 nums =", nums)
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""" 遍历数组 """
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traverse(nums)
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""" 查找元素 """
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index = find(nums, 3)
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print("在 nums 中查找元素 3 ，得到索引 =", index)
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@ -8,3 +8,72 @@ import sys, os.path as osp
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sys.path.append(osp.dirname(osp.dirname(osp.abspath(__file__))))
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from include import *
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""" 在链表的结点 n0 之后插入结点 P """
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def insert(n0, P):
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n1 = n0.next
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n0.next = P
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P.next = n1
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""" 删除链表的结点 n0 之后的首个结点 """
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def remove(n0):
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if not n0.next:
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return
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# n0 -> P -> n1
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P = n0.next
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n1 = P.next
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n0.next = n1
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""" 访问链表中索引为 index 的结点 """
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def access(head, index):
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for _ in range(index):
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head = head.next
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if not head:
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return None
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return head
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""" 在链表中查找值为 target 的首个结点 """
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def find(head, target):
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index = 0
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while head:
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if head.val == target:
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return index
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head = head.next
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index += 1
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return -1
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"""
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Driver Code
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"""
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if __name__ == "__main__":
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""" 初始化链表 """
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# 初始化各个结点
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n0 = ListNode(1)
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n1 = ListNode(3)
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n2 = ListNode(2)
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n3 = ListNode(5)
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n4 = ListNode(4)
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# 构建引用指向
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n0.next = n1
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n1.next = n2
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n2.next = n3
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n3.next = n4
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print("初始化的链表为")
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print_linked_list(n0)
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""" 插入结点 """
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insert(n0, ListNode(0))
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print("插入结点后的链表为")
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print_linked_list(n0)
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""" 删除结点 """
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remove(n0)
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print("删除结点后的链表为")
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print_linked_list(n0)
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""" 访问结点 """
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node = access(n0, 3)
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print("链表中索引 3 处的结点的值 = {}".format(node.val))
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""" 查找结点 """
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index = find(n0, 2)
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print("链表中值为 2 的结点的索引 = {}".format(index))
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@ -8,3 +8,57 @@ import sys, os.path as osp
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sys.path.append(osp.dirname(osp.dirname(osp.abspath(__file__))))
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from include import *
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"""
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Driver Code
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"""
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if __name__ == "__main__":
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""" 初始化列表 """
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list = [1, 3, 2, 5, 4]
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print("列表 list =", list)
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""" 访问元素 """
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num = list[1]
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print("访问索引 1 处的元素，得到 num =", num)
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""" 更新元素 """
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list[1] = 0
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print("将索引 1 处的元素更新为 0 ，得到 list =", list)
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""" 清空列表 """
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list.clear()
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print("清空列表后 list =", list)
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""" 尾部添加元素 """
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list.append(1)
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list.append(3)
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list.append(2)
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list.append(5)
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list.append(4)
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print("添加元素后 list = ", list)
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""" 中间插入元素 """
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list.insert(3, 6)
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print("在索引 3 处插入数字 6 ，得到 list =", list)
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""" 删除元素 """
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list.pop(3)
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print("删除索引 3 处的元素，得到 list =", list)
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""" 通过索引遍历列表 """
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count = 0
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for i in range(len(list)):
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count += 1
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""" 直接遍历列表元素 """
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count = 0
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for n in list:
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count += 1
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""" 拼接两个列表 """
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list1 = [6, 8, 7, 10, 9]
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list += list1
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print("将列表 list1 拼接到 list 之后，得到 list =", list)
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""" 排序列表 """
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list.sort()
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print("排序列表后 list =", list)
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@ -8,3 +8,103 @@ import sys, os.path as osp
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sys.path.append(osp.dirname(osp.dirname(osp.abspath(__file__))))
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from include import *
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""" 列表类简易实现 """
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class MyList:
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""" 构造函数 """
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def __init__(self):
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self._initial_capacity = 10 # 列表初始容量
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self._nums = [0] * self._initial_capacity # 数组（存储列表元素）
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self._size = 0 # 列表长度（即当前元素数量）
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self._extend_ratio = 2 # 每次列表扩容的倍数
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""" 获取列表长度（即当前元素数量） """
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def size(self):
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return self._size
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""" 获取列表容量 """
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def capacity(self):
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return len(self._nums)
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""" 访问元素 """
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def get(self, index):
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# 索引如果越界则抛出异常，下同
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assert index < self._size, "索引越界"
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return self._nums[index]
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""" 更新元素 """
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def set(self, num, index):
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assert index < self._size, "索引越界"
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self._nums[index] = num
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""" 中间插入元素 """
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def add(self, num, index=-1):
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assert index < self._size, "索引越界"
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if index == -1:
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index = self._size
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# 元素数量超出容量时，触发扩容机制
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if self._size == self.capacity():
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self.extend_capacity()
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# 索引 i 以及之后的元素都向后移动一位
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for j in range(self._size - 1, index - 1, -1):
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self._nums[j + 1] = self._nums[j]
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self._nums[index] = num
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# 更新元素数量
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self._size += 1
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""" 删除元素 """
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def remove(self, index):
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assert index < self._size, "索引越界"
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# 索引 i 之后的元素都向前移动一位
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for j in range(index, self._size - 1):
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self._nums[j] = self._nums[j + 1]
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# 更新元素数量
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self._size -= 1
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""" 列表扩容 """
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def extend_capacity(self):
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# 新建一个长度为 self._size 的数组，并将原数组拷贝到新数组
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self._nums = self._nums + [0] * self.capacity() * (self._extend_ratio - 1)
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""" 返回有效长度的列表 """
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def to_array(self):
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return self._nums[:self._size]
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"""
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Driver Code
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"""
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if __name__ == "__main__":
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""" 初始化列表 """
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list = MyList()
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""" 尾部添加元素 """
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list.add(1)
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list.add(3)
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list.add(2)
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list.add(5)
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list.add(4)
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print("列表 list = {} ，容量 = {} ，长度 = {}"
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.format(list.to_array(), list.capacity(), list.size()))
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""" 中间插入元素 """
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list.add(num=6, index=3)
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print("在索引 3 处插入数字 6 ，得到 list =", list.to_array())
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""" 删除元素 """
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list.remove(3)
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print("删除索引 3 处的元素，得到 list =", list.to_array())
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""" 访问元素 """
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num = list.get(1)
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print("访问索引 1 处的元素，得到 num =", num)
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""" 更新元素 """
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list.set(0, 1)
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print("将索引 1 处的元素更新为 0 ，得到 list =", list.to_array())
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""" 测试扩容机制 """
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for i in range(10):
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# 在 i = 5 时，列表长度将超出列表容量，此时触发扩容机制
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list.add(i)
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print("扩容后的列表 list = {} ，容量 = {} ，长度 = {}"
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.format(list.to_array(), list.capacity(), list.size()))
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@ -33,7 +33,9 @@ comments: true
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=== "Python"
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```python title="array.py"
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""" 初始化数组 """
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arr = [0] * 5 # [ 0, 0, 0, 0, 0 ]
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nums = [1, 3, 2, 5, 4]
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```
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## 数组优点
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@ -74,7 +76,13 @@ elementAddr = firtstElementAddr + elementLength * elementIndex
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=== "Python"
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```python title="array.py"
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""" 随机访问元素 """
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def randomAccess(nums):
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# 在区间 [0, len(nums)) 中随机抽取一个数字
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random_index = random.randint(0, len(nums))
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# 获取并返回随机元素
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random_num = nums[random_index]
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return random_num
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```
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## 数组缺点
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@ -106,7 +114,15 @@ elementAddr = firtstElementAddr + elementLength * elementIndex
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=== "Python"
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```python title="array.py"
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""" 扩展数组长度 """
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def extend(nums, enlarge):
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# 初始化一个扩展长度后的数组
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res = [0] * (len(nums) + enlarge)
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# 将原数组中的所有元素复制到新数组
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for i in range(len(nums)):
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res[i] = nums[i]
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# 返回扩展后的新数组
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return res
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```
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**数组中插入或删除元素效率低下。** 假设我们想要在数组中间某位置插入一个元素，由于数组元素在内存中是 “紧挨着的” ，它们之间没有空间再放任何数据。因此，我们不得不将此索引之后的所有元素都向后移动一位，然后再把元素赋值给该索引。删除元素也是类似，需要把此索引之后的元素都向前移动一位。总体看有以下缺点：
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@ -150,7 +166,19 @@ elementAddr = firtstElementAddr + elementLength * elementIndex
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=== "Python"
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```python title="array.py"
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""" 在数组的索引 index 处插入元素 num """
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def insert(nums, num, index):
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# 把索引 index 以及之后的所有元素向后移动一位
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for i in range(len(nums) - 1, index - 1, -1):
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nums[i] = nums[i - 1]
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# 将 num 赋给 index 处元素
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nums[index] = num
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""" 删除索引 index 处元素 """
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def remove(nums, index):
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# 把索引 index 之后的所有元素向前移动一位
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for i in range(index, len(nums) - 1):
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nums[i] = nums[i + 1]
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```
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## 数组常用操作
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@ -183,7 +211,15 @@ elementAddr = firtstElementAddr + elementLength * elementIndex
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=== "Python"
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```python title="array.py"
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""" 遍历数组 """
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def traverse(nums):
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count = 0
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# 通过索引遍历数组
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for i in range(len(nums)):
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count += 1
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# 直接遍历数组
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for num in nums:
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count += 1
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```
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**数组查找。** 通过遍历数组，查找数组内的指定元素，并输出对应索引。
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@ -210,7 +246,12 @@ elementAddr = firtstElementAddr + elementLength * elementIndex
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=== "Python"
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```python title="array.py"
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""" 在数组中查找指定元素 """
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def find(nums, target):
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for i in range(len(nums)):
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if nums[i] == target:
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return i
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return -1
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```
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## 数组典型应用
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@ -77,7 +77,18 @@ comments: true
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=== "Python"
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```python title=""
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""" 初始化链表 1 -> 3 -> 2 -> 5 -> 4 """
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# 初始化各个结点
|
||||
n0 = ListNode(1)
|
||||
n1 = ListNode(3)
|
||||
n2 = ListNode(2)
|
||||
n3 = ListNode(5)
|
||||
n4 = ListNode(4)
|
||||
# 构建引用指向
|
||||
n0.next = n1
|
||||
n1.next = n2
|
||||
n2.next = n3
|
||||
n3.next = n4
|
||||
```
|
||||
|
||||
## 链表优点
|
||||
|
|
@ -118,7 +129,20 @@ comments: true
|
|||
=== "Python"
|
||||
|
||||
```python title=""
|
||||
""" 在链表的结点 n0 之后插入结点 P """
|
||||
def insert(n0, P):
|
||||
n1 = n0.next
|
||||
n0.next = P
|
||||
P.next = n1
|
||||
|
||||
""" 删除链表的结点 n0 之后的首个结点 """
|
||||
def remove(n0):
|
||||
if not n0.next:
|
||||
return
|
||||
# n0 -> P -> n1
|
||||
P = n0.next
|
||||
n1 = P.next
|
||||
n0.next = n1
|
||||
```
|
||||
|
||||
## 链表缺点
|
||||
|
|
@ -148,7 +172,13 @@ comments: true
|
|||
=== "Python"
|
||||
|
||||
```python title=""
|
||||
|
||||
""" 访问链表中索引为 index 的结点 """
|
||||
def access(head, index):
|
||||
for _ in range(index):
|
||||
head = head.next
|
||||
if not head:
|
||||
return None
|
||||
return head
|
||||
```
|
||||
|
||||
**链表的内存占用多。** 链表以结点为单位，每个结点除了保存值外，还需额外保存指针（引用）。这意味着同样数据量下，链表比数组需要占用更多内存空间。
|
||||
|
|
@ -182,7 +212,15 @@ comments: true
|
|||
=== "Python"
|
||||
|
||||
```python title=""
|
||||
|
||||
""" 在链表中查找值为 target 的首个结点 """
|
||||
def find(head, target):
|
||||
index = 0
|
||||
while head:
|
||||
if head.val == target:
|
||||
return index
|
||||
head = head.next
|
||||
index += 1
|
||||
return -1
|
||||
```
|
||||
|
||||
## 常见链表类型
|
||||
|
|
@ -214,7 +252,12 @@ comments: true
|
|||
=== "Python"
|
||||
|
||||
```python title=""
|
||||
|
||||
""" 双向链表结点类 """
|
||||
class ListNode:
|
||||
def __init__(self, x):
|
||||
self.val = x # 结点值
|
||||
self.next = None # 指向后继结点的指针（引用）
|
||||
self.prev = None # 指向前驱结点的指针（引用）
|
||||
```
|
||||
|
||||
|
||||
|
|
|
|||
|
|
@ -30,7 +30,8 @@ comments: true
|
|||
=== "Python"
|
||||
|
||||
```python title="list.py"
|
||||
|
||||
""" 初始化列表 """
|
||||
list = [1, 3, 2, 5, 4]
|
||||
```
|
||||
|
||||
**访问与更新元素。** 列表的底层数据结构是数组，因此可以在 $O(1)$ 时间内访问与更新元素，效率很高。
|
||||
|
|
@ -54,7 +55,11 @@ comments: true
|
|||
=== "Python"
|
||||
|
||||
```python title="list.py"
|
||||
""" 访问元素 """
|
||||
num = list[1] # 访问索引 1 处的元素
|
||||
|
||||
""" 更新元素 """
|
||||
list[1] = 0 # 将索引 1 处的元素更新为 0
|
||||
```
|
||||
|
||||
**在列表中添加、插入、删除元素。** 相对于数组，列表可以自由地添加与删除元素。在列表尾部添加元素的时间复杂度为 $O(1)$ ，但是插入与删除元素的效率仍与数组一样低，时间复杂度为 $O(N)$ 。
|
||||
|
|
@ -88,7 +93,21 @@ comments: true
|
|||
=== "Python"
|
||||
|
||||
```python title="list.py"
|
||||
""" 清空列表 """
|
||||
list.clear()
|
||||
|
||||
""" 尾部添加元素 """
|
||||
list.append(1)
|
||||
list.append(3)
|
||||
list.append(2)
|
||||
list.append(5)
|
||||
list.append(4)
|
||||
|
||||
""" 中间插入元素 """
|
||||
list.insert(3, 6) # 在索引 3 处插入数字 6
|
||||
|
||||
""" 删除元素 """
|
||||
list.pop(3) # 删除索引 3 处的元素
|
||||
```
|
||||
|
||||
**遍历列表。** 与数组一样，列表可以使用索引遍历，也可以使用 `for-each` 直接遍历。
|
||||
|
|
@ -118,7 +137,15 @@ comments: true
|
|||
=== "Python"
|
||||
|
||||
```python title="list.py"
|
||||
""" 通过索引遍历列表 """
|
||||
count = 0
|
||||
for i in range(len(list)):
|
||||
count += 1
|
||||
|
||||
""" 直接遍历列表元素 """
|
||||
count = 0
|
||||
for n in list:
|
||||
count += 1
|
||||
```
|
||||
|
||||
**拼接两个列表。** 再创建一个新列表 `list1` ，我们可以将其中一个列表拼接到另一个的尾部。
|
||||
|
|
@ -140,7 +167,9 @@ comments: true
|
|||
=== "Python"
|
||||
|
||||
```python title="list.py"
|
||||
|
||||
""" 拼接两个列表 """
|
||||
list1 = [6, 8, 7, 10, 9]
|
||||
list += list1 # 将列表 list1 拼接到 list 之后
|
||||
```
|
||||
|
||||
**排序列表。** 排序也是常用的方法之一，完成列表排序后，我们就可以使用在数组类算法题中经常考察的「二分查找」和「双指针」算法了。
|
||||
|
|
@ -161,7 +190,8 @@ comments: true
|
|||
=== "Python"
|
||||
|
||||
```python title="list.py"
|
||||
|
||||
""" 排序列表 """
|
||||
list.sort() # 排序后，列表元素从小到大排列
|
||||
```
|
||||
|
||||
## 列表简易实现 *
|
||||
|
|
@ -189,12 +219,12 @@ comments: true
|
|||
nums = new int[initialCapacity];
|
||||
}
|
||||
|
||||
/* 获取列表容量 */
|
||||
/* 获取列表长度（即当前元素数量）*/
|
||||
public int size() {
|
||||
return size;
|
||||
}
|
||||
|
||||
/* 获取列表长度（即当前元素数量） */
|
||||
/* 获取列表容量 */
|
||||
public int capacity() {
|
||||
return nums.length;
|
||||
}
|
||||
|
|
@ -269,5 +299,60 @@ comments: true
|
|||
=== "Python"
|
||||
|
||||
```python title="my_list.py"
|
||||
""" 列表类简易实现 """
|
||||
class MyList:
|
||||
""" 构造函数 """
|
||||
def __init__(self):
|
||||
self._initial_capacity = 10 # 列表初始容量
|
||||
self._nums = [0] * self._initial_capacity # 数组（存储列表元素）
|
||||
self._size = 0 # 列表长度（即当前元素数量）
|
||||
self._extend_ratio = 2 # 每次列表扩容的倍数
|
||||
|
||||
""" 获取列表长度（即当前元素数量） """
|
||||
def size(self):
|
||||
return self._size
|
||||
|
||||
""" 获取列表容量 """
|
||||
def capacity(self):
|
||||
return len(self._nums)
|
||||
|
||||
""" 访问元素 """
|
||||
def get(self, index):
|
||||
# 索引如果越界则抛出异常，下同
|
||||
assert index < self._size, "索引越界"
|
||||
return self._nums[index]
|
||||
|
||||
""" 更新元素 """
|
||||
def set(self, num, index):
|
||||
assert index < self._size, "索引越界"
|
||||
self._nums[index] = num
|
||||
|
||||
""" 中间插入元素 """
|
||||
def add(self, num, index=-1):
|
||||
assert index < self._size, "索引越界"
|
||||
if index == -1:
|
||||
index = self._size
|
||||
# 元素数量超出容量时，触发扩容机制
|
||||
if self._size == self.capacity():
|
||||
self.extend_capacity()
|
||||
# 索引 i 以及之后的元素都向后移动一位
|
||||
for j in range(self._size - 1, index - 1, -1):
|
||||
self._nums[j + 1] = self._nums[j]
|
||||
self._nums[index] = num
|
||||
# 更新元素数量
|
||||
self._size += 1
|
||||
|
||||
""" 删除元素 """
|
||||
def remove(self, index):
|
||||
assert index < self._size, "索引越界"
|
||||
# 索引 i 之后的元素都向前移动一位
|
||||
for j in range(index, self._size - 1):
|
||||
self._nums[j] = self._nums[j + 1]
|
||||
# 更新元素数量
|
||||
self._size -= 1
|
||||
|
||||
""" 列表扩容 """
|
||||
def extend_capacity(self):
|
||||
# 新建一个长度为 self._size 的数组，并将原数组拷贝到新数组
|
||||
self._nums = self._nums + [0] * self.capacity() * (self._extend_ratio - 1)
|
||||
```
|
||||
|
|
|
|||
Loading…
Reference in a new issue