BinarySearch

int BinarySearch(int* arr, int start, int end, int key) {
    if (start > end) return -1;
    
    int mid = (start + end) / 2;
 
    if (arr[mid] == key) return mid;
    else if (arr[mid] < key) return BinarySearch(arr, start, mid - 1, key);
    else return BinarySearch(arr, mid + 1, end, key);
 
}