DSA Problem Solution: 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.

Example 1:

Input: nums = [-6,1,3,5,9,11], target = 9

Output: 4

Explanation: 9 exists in nums and its index is 4

Example 2:

Input: nums = [-2,0,3,6,9,20], target = 2

Output: -1

Explanation: 2 does not exist in nums so return -1

public class Solution {
    public int Search(int[] nums, int target) {
     return binarySearch(0,nums.Length-1, nums,target);
    }

    public int binarySearch(int startIndex, int lastIndex,int[] nums, int target)
    {
     if(startIndex>=lastIndex)
     {         
         return nums[startIndex]==target?startIndex:-1;
     }
     
      int mid = (startIndex+lastIndex)/2;

      if(nums[mid]==target)
      {
          return mid;
      }
      else if(nums[mid]>target)
      {
         return binarySearch(startIndex,mid-1, nums,target);
      }
      else {
          return binarySearch(mid+1,lastIndex,nums,target);
      }
     
    }
}