50 lines
1.5 KiB
Python
50 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
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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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"""二分搜尋最左一個 target"""
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# 等價於查詢 target 的插入點
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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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"""二分搜尋最右一個 target"""
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# 轉化為查詢最左一個 target + 1
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i = binary_search_insertion(nums, target + 1)
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# j 指向最右一個 target ，i 指向首個大於 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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# 包含重複元素的陣列
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nums = [1, 3, 6, 6, 6, 6, 6, 10, 12, 15]
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print(f"\n陣列 nums = {nums}")
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# 二分搜尋左邊界和右邊界
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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"最左一個元素 {target} 的索引為 {index}")
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index = binary_search_right_edge(nums, target)
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print(f"最右一個元素 {target} 的索引為 {index}")
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