BinarySearch.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.

public class BinarySearch {
    public int search(int[] nums, int target) {
        int lo = 0;
        int hi = nums.length - 1;

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

    public static void main(String[] args) {
        BinarySearch bs = new BinarySearch();
        int[] nums = {-1, 0, 3, 5, 9, 12};
        System.out.println(bs.search(nums, 9));
    }
}