704. Binary Search.java

/*
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:

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

//Soution:
class Solution {
    public int search(int[] nums, int target) {
        if(nums.length == 0) return 0;
        int start = 0;
        int end = nums.length - 1;
        while(start <= end){
            int mid = start + (end-start)/2;
            if(nums[mid] > target){
                end = mid - 1;
            }else if(nums[mid] < target){
                start = mid + 1;
            }else{
                return mid;
            }
        }
        return -1;
        
    }
}