algorithm - 查找

int binary_search_f(std::vector<int> &src, int value, int l, int r) {
  if (l > r) {
    return -1;
  }

  int mid = (l + r) / 2;

  if (value == src[mid]) {
    return mid;
  } else if (value > src[mid]) {
    return binary_search_f(src, value, mid + 1, r);
  }
  return binary_search_f(src, value, l, mid - 1);
}

int binary_search(std::vector<int> &src, int value) {
  return binary_search_f(src, value, 0, src.size() - 1);
}