leetcode704. Binary Search

兔兔爱学习兔兔爱学习2024-10-22 16:04

Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1.

You must write an algorithm with O(log n) runtime complexity.

Example 1:

Input: nums = $-1,0,3,5,9,12$ , target = 9

Output: 4

Explanation: 9 exists in nums and its index is 4

Example 2:

Input: nums = $-1,0,3,5,9,12$ , target = 2

Output: -1

Explanation: 2 does not exist in nums so return -1

Constraints:

复制代码

1 <= nums.length <= 104
-104 < nums[i], target < 104
All the integers in nums are unique.
nums is sorted in ascending order.

https://leetcode.cn/problems/binary-search/description/

思路：二分查找

「二分查找」是利用数组的有序性，每轮缩窄一半的查找区间（即排除一半元素），直到找到目标值或查找区间为空时返回。

python 复制代码

class Solution:
    def search(self, nums: List[int], target: int) -> int:
        i, j = 0, len(nums) - 1
        while i <= j:
            m = (i + j) // 2
            if nums[m] < target: i = m + 1
            elif nums[m] > target: j = m - 1
            else: return m
        return -1