c_cpp 组合 - 枚举所有

Posted 2021-05-14

// Trick: initialize a vector of k 1's, then resize to 'n' and fill with 0's
// use next_permutation (in reverse) to "bitmask" and enumerate all options
int enumerate_combinations(int n, int k, vector<int> &A) {
  vector<int>  b(k, 1);
  b.resize(n, 0);

  // very basic, store count
  int cnt = 0;

  do {
    // pass over all n items, take/save/print the ones that match the "bitmask"
    for (int i = 0; i < n; i++) {
      if (b[i]) {
        cout << A[i] << " ";
      }
    }
    cnt++;
    cout << endl;

  } while (next_permutation(b.rbegin(), b.rend()));

  return cnt;
}