704. Binary Search

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

Solution:

class Solution {
    public int search(int[] nums, int target) {
        if (nums == null || nums.length == 0){
            return -1;
        }

        int left = 0;
        int right = nums.length -1;

        while(left <= right){
            int mid = left + (right - left)/2;
            if (nums[mid] == target){
                return mid;
            }else if (nums[mid] < target){
                left = mid + 1;
            }else{
                right = mid - 1;
            }
        }

        return - 1;

    }
}

// TC: O(logn)
// SC: O(1)