Bridge Link solution

bridge_link.cpp

//https://www.acmicpc.net/problem/1010
//time complexity : O(N)
//space complexity : O(1)

#include <stdio.h>

int combination(int west, int east) {
  if (west >= 30 || east >= 30 || west > east)
    return -1;

  if (west == 0) return 0;

  int ret = 1;
  for(int i = 1; i <= west; i++)
   ret = ret * (east - i + 1) / i;

  return ret;
}

int main() {
  int T;
  scanf("%d", &T);

  while(T-- > 0) {
    int N, M;

    scanf("%d %d", &N, &M);
    printf("%d\n", combination(N, M));
  }

  return 0;
}