704 Binary Search

LeetCode

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

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最最普通的二分查找，时间复杂度 o(log n) ，空间复杂度 o(1)

public int search(int[] nums, int target) {
    int left=0, right=nums.length-1;
    int mid, t;
    while(left<=right){
        mid = (left+right)/2;
        t = nums[mid];
        if(t<target){
            left = mid + 1;
        } else if (t>target){
            right = mid - 1;
        } else {
            return mid;
        }
    }
    return -1;
}