704. Binary Search

Leetcode Binary Search

Given a sorted (in ascending order) integer array nums of $n$ elements and a target value, write a function to search target in nums. If target exists, then return its index, otherwise return -1.

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

Note:

• You may assume that all elements in nums are unique.
• $n$ will be in the range [1, 10000].
• The value of each element in nums will be in the range [-9999, 9999].

分析

标准的二分查找。

public int search(int[] nums, int target) {
    if (nums == null || nums.length == 0) return -1;
    int lo = 0, hi = nums.length - 1;
    while (lo <= hi) {
        int mid = lo + (hi - lo) / 2;
        int cmp = nums[mid] - target;
        if (cmp > 0) hi = mid - 1;
        else if (cmp < 0) lo = mid + 1;
        else return mid;
    }
    return -1;
}