hello-algo/codes/python/chapter_divide_and_conquer/binary_search_recur.py
2023-07-17 03:48:33 +08:00

39 lines
1.1 KiB
Python

"""
File: binary_search_recur.py
Created Time: 2023-07-17
Author: krahets (xisunyy@163.com)
"""
def dfs(nums: list[int], target: int, i: int, j: int) -> int:
"""二分查找:分治"""
# 若区间为空,代表未找到目标元素,则返回 -1
if i > j:
return -1
# 计算中点索引 m
m = (i + j) // 2
if nums[m] < target:
# 此情况说明 target 在区间 [m+1, j] 中,递归解决该子问题
return dfs(nums, target, m + 1, j)
elif nums[m] > target:
# 此情况说明 target 在区间 [i, m-1] 中,递归解决该子问题
return dfs(nums, target, i, m - 1)
else:
# 找到目标元素,返回其索引
return m
def binary_search(nums: list[int], target: int) -> int:
"""二分查找"""
n = len(nums)
return dfs(nums, target, 0, n - 1)
"""Driver Code"""
if __name__ == "__main__":
target = 6
nums = [1, 3, 6, 8, 12, 15, 23, 26, 31, 35]
# 二分查找(双闭区间)
index: int = binary_search(nums, target)
print("目标元素 6 的索引 = ", index)