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53 lines
1.8 KiB
Python
53 lines
1.8 KiB
Python
"""
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File: binary_search_edge.py
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Created Time: 2023-05-18
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Author: Krahets (krahets@163.com)
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"""
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def binary_search_left_edge(nums: list[int], target: int) -> int:
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"""二分查找最左一个元素"""
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# 初始化双闭区间 [0, n-1] ，即 i, j 分别指向数组首元素、尾元素
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i, j = 0, len(nums) - 1
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while i <= j:
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m = (i + j) // 2 # 计算中点索引 m
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if nums[m] < target:
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i = m + 1 # target 在区间 [m+1, j] 中
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elif nums[m] > target:
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j = m - 1 # target 在区间 [i, m-1] 中
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else:
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j = m - 1 # 首个小于 target 的元素在区间 [i, m-1] 中
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if i == len(nums) or nums[i] != target:
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return -1 # 未找到目标元素，返回 -1
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return i
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def binary_search_right_edge(nums: list[int], target: int) -> int:
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"""二分查找最右一个元素"""
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# 初始化双闭区间 [0, n-1] ，即 i, j 分别指向数组首元素、尾元素
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i, j = 0, len(nums) - 1
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while i <= j:
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m = (i + j) // 2 # 计算中点索引 m
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if nums[m] < target:
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i = m + 1 # target 在区间 [m+1, j] 中
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elif nums[m] > target:
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j = m - 1 # target 在区间 [i, m-1] 中
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else:
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i = m + 1 # 首个大于 target 的元素在区间 [m+1, j] 中
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if j == len(nums) or nums[j] != target:
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return -1 # 未找到目标元素，返回 -1
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return j
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"""Driver Code"""
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if __name__ == "__main__":
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target = 6
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nums = [1, 3, 6, 6, 6, 6, 6, 10, 12, 15]
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# 二分查找最左一个元素
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index_left = binary_search_left_edge(nums, target)
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print("数组中最左一个元素 6 的索引 = ", index_left)
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# 二分查找最右一个元素
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index_right = binary_search_right_edge(nums, target)
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print("数组中最右一个元素 6 的索引 = ", index_right)
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