Binary Search Upper Lower Bound

Binary Search Algorithm - Binary Search is simple yet efficient algorithm for searching an element is a sorted array. In this video, Prateek bhayia explains how to find Upper and Lower Bound of Binary Search.

#include<iostream>
using namespace std;


int lowerBound(int *a,int n,int key){
    int s =0,e=n-1;
    int ans = -1;

    while(s<=e){
        int mid = (s+e)/2;

        if(a[mid]==key){
            ans = mid;
            e = mid - 1;
        }
        else if(a[mid]>key){
            e = mid - 1;
        }
        else{
            s = mid + 1;
        }
    }

    return ans;
}

int upperBound(int *a,int n,int key){
    int s =0,e=n-1;
    int ans = -1;

    while(s<=e){
        int mid = (s+e)/2;

        if(a[mid]==key){
            ans = mid;
            s = mid+1;
        }
        else if(a[mid]>key){
            e = mid - 1;
        }
        else{
            s = mid + 1;
        }
    }

    return ans;
}

int main(){
    int a[] = {1,2,2,2,2,2,3,3,3,5,5,5};
    int n = sizeof(a)/sizeof(int);
    cout<<lowerBound(a,n,2)<<endl;
    cout<<upperBound(a,n,2)<<endl;


return 0;
}