mirror of
https://github.com/krahets/hello-algo.git
synced 2024-12-27 20:56:29 +08:00
50 lines
1.5 KiB
Python
50 lines
1.5 KiB
Python
|
"""
|
|||
|
|
File: binary_search_edge.py
|
|||
|
|
Created Time: 2023-08-04
|
|||
|
|
Author: krahets (krahets@163.com)
|
|||
|
|
"""
|
|||
|
|
|
|||
|
|
import sys
|
|||
|
|
from pathlib import Path
|
|||
|
|
|
|||
|
|
sys.path.append(str(Path(__file__).parent.parent))
|
|||
|
|
from binary_search_insertion import binary_search_insertion
|
|||
|
|
|
|||
|
|
|
|||
|
|
def binary_search_left_edge(nums: list[int], target: int) -> int:
|
|||
|
|
"""二分搜尋最左一個 target"""
|
|||
|
|
# 等價於查詢 target 的插入點
|
|||
|
|
i = binary_search_insertion(nums, target)
|
|||
|
|
# 未找到 target ，返回 -1
|
|||
|
|
if i == len(nums) or nums[i] != target:
|
|||
|
|
return -1
|
|||
|
|
# 找到 target ，返回索引 i
|
|||
|
|
return i
|
|||
|
|
|
|||
|
|
|
|||
|
|
def binary_search_right_edge(nums: list[int], target: int) -> int:
|
|||
|
|
"""二分搜尋最右一個 target"""
|
|||
|
|
# 轉化為查詢最左一個 target + 1
|
|||
|
|
i = binary_search_insertion(nums, target + 1)
|
|||
|
|
# j 指向最右一個 target ，i 指向首個大於 target 的元素
|
|||
|
|
j = i - 1
|
|||
|
|
# 未找到 target ，返回 -1
|
|||
|
|
if j == -1 or nums[j] != target:
|
|||
|
|
return -1
|
|||
|
|
# 找到 target ，返回索引 j
|
|||
|
|
return j
|
|||
|
|
|
|||
|
|
|
|||
|
|
"""Driver Code"""
|
|||
|
|
if __name__ == "__main__":
|
|||
|
|
# 包含重複元素的陣列
|
|||
|
|
nums = [1, 3, 6, 6, 6, 6, 6, 10, 12, 15]
|
|||
|
|
print(f"\n陣列 nums = {nums}")
|
|||
|
|
|
|||
|
|
# 二分搜尋左邊界和右邊界
|
|||
|
|
for target in [6, 7]:
|
|||
|
|
index = binary_search_left_edge(nums, target)
|
|||
|
|
print(f"最左一個元素 {target} 的索引為 {index}")
|
|||
|
|
index = binary_search_right_edge(nums, target)
|
|||
|
|
print(f"最右一個元素 {target} 的索引為 {index}")
|