#include<cstring>  #include<iostream>  #define LEN 10  using namespace std;  char elem[LEN] = { 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j' };  char result[LEN];  bool filled[LEN];  void permutation(int k, int n) {      if (k == n) {          for (int i = 0; i < n; i++) {              cout << result[i] << " ";             }          cout << endl;      } else {          for (int i = 0; i < n; i++) {              if (!filled[i]) {                  filled[i] = true;                  result[k] = elem[i];                  permutation(k + 1, n);                  filled[i] = false;              }          }      }  }  int main() {      memset(result, 0, sizeof(result));      memset(filled, false, sizeof(filled));      permutation(0, LEN);      return 0;  }