Binary Search

Binary Search

Problem Statement

Given a sorted array of size N and an integer K, find the position at which K is present in the array using binary search.

Example 1

Input :
N = 5
arr[] = {1 2 3 4 5} 
K = 4

Output : 3

Explanation :
4 appears at index 3.

Example 2

Input :
N = 5
arr[] = {11 22 33 44 55} 
K = 445

Output : -1

Explanation :
445 is not present.

Task

You dont need to read input or print anything. Complete the function binarysearch() which takes arr[], N and K as input parameters and returns the index of K in the array. If K is not present in the array, return -1.

Expected Time Complexity : O(LogN)
Expected Auxiliary Space : O(LogN) if solving recursively and O(1) otherwise.

Constraints :
1 <= N <= 10⁵
1 <= arr[i] <= 10⁶
1 <= K <= 10⁶

Solutions

Java Solution

class Solution {
    int binarysearch(int arr[], int n, int k) {
        // code here
        int low = 0, high = n - 1;
        int mid;
        while(low <= high) {
            mid = (low + high)/2;
            if(k == arr[mid]) {
                return mid;
            }
            else if(k > arr[mid]) {
                low = mid + 1;
            }
            else {
                high = mid - 1;
            }
        }
        return -1;
    }
}
        
    

C++ Solution

class Solution {
public:
	int binarysearch(int arr[], int n, int k) {
 		int low = 0, high = n - 1;
        int mid;
        while(low <= high) {
            mid = (low + high)/2;
            if(k == arr[mid]) {
                return mid;
            }
            else if(k > arr[mid]) {
                low = mid + 1;
            }
            else {
                high = mid - 1;
            }
        }
        return -1;
 	}
};