704. Binary Search - Easy

Posted 2021-01-27 fatttcat

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

 

classical binary search

time: O(log(n)), space: O(1)

class Solution {
    public int search(int[] nums, int target) {
        if(nums == null || nums.length == 0) return -1;
        int l = 0, r = nums.length - 1;
        while(l <= r) {
            int m = l + (r - l) / 2;
            if(nums[m] == target)
                return m;
            else if(nums[m] > target)
                r = m - 1;
            else
                l = m + 1;
        }
        return -1;
    }
}