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48 lines
1.5 KiB
Python
48 lines
1.5 KiB
Python
"""
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File: binary_search_edge.py
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Created Time: 2023-08-04
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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 binary_search_insertion import binary_search_insertion
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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 target"""
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# 等价于查找 target 的插入点
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i = binary_search_insertion(nums, target)
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# 未找到 target ，返回 -1
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if i == len(nums) or nums[i] != target:
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return -1
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# 找到 target ，返回索引 i
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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 target"""
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# 转化为查找最左一个 target + 1
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i = binary_search_insertion(nums, target + 1)
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# j 指向最右一个 target ，i 指向首个大于 target 的元素
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j = i - 1
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# 未找到 target ，返回 -1
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if j == -1 or nums[j] != target:
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return -1
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# 找到 target ，返回索引 j
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return j
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"""Driver Code"""
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if __name__ == "__main__":
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# 包含重复元素的数组
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nums = [1, 3, 6, 6, 6, 6, 6, 10, 12, 15]
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print(f"\n数组 nums = {nums}")
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# 二分查找左边界和右边界
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for target in [6, 7]:
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index = binary_search_left_edge(nums, target)
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print(f"最左一个元素 {target} 的索引为 {index}")
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index = binary_search_right_edge(nums, target)
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print(f"最右一个元素 {target} 的索引为 {index}")
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