64 lines
2.2 KiB
Python
64 lines
2.2 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
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from pathlib import Path
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sys.path.append(str(Path(__file__).parent.parent))
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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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def binary_search_edge(nums: list[int], target: int) -> int:
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"""二分查找target左右边界"""
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# 当数组中不包含target时,索引i,j最终分别指向首个大于,小于target的元素
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# 左侧边界查找 = 查找target-0.5 ;返回索引i
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# 右侧边界查找 = 查找target+0.5 ;返回索引j
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i = binary_search_insertion(nums, target - 0.5)
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j = binary_search_insertion(nums, target + 0.5) - 1
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# 当数组中存在元素target时,左侧边界<=右侧边界
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if i > j:
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return -1, -1
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else:
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return i, 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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# 二分查找左右边界
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for target1 in [6,8,10]:
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left_index,right_index = binary_search_edge(nums, target1)
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print(f"元素 {target1} 的左右边界索引分别为 {left_index}, {right_index}") |