PermutationAndCombination.java

// Arrangement or Permutation
int P(int n, int m) {
  int res = 1;
  int limit = n - m;
  while (n > limit) {
    res *= n--;
  }
  return res;
}

// Combination
int C(int n, int m) {
  m = Math.min(m, n - m);
  int res = P(n, m);
  while (m > 0) {
    res /= m--;
  }
  return res;
}