BinSearch

int BinSearch(int *arr, int begin, int end, int x) {
  while (begin <= end) {
    int mid = begin + (end - begin) / 2;
    if (arr[mid] == x) {
      return mid;
    } else if (arr[mid] < x) {
      begin = mid + 1;
    } else {
      end = mid - 1;
    }
  }
  return -1;
}