Problem p00469 (C++)

Buggy submission (status: Time Limit Exceeded):
/* {{{ Shinobu kawaii */
/*
  ______   __        _                  __
.' ____ \ [  |      (_)                [  |
| (___ \_| | |--.   __   _ .--.   .--.  | |.--.   __   _
 _.____`.  | .-. | [  | [ `.-. |/ .'`\ \| '/'`\ \[  | | |
| \____) | | | | |  | |  | | | || \__. ||  \__/ | | \_/ |,
 \______.'[___]|__][___][___||__]'.__.'[__;.__.'  '.__.'_/

*/
/* }}} */

#include <bits/stdc++.h>
using namespace std;

// #define int long long
struct Fast {
  Fast() {
    std::cin.tie(0);
    ios::sync_with_stdio(false);
  }
} fast;

/* cpp template {{{ */

/* short */
#define pb push_back
#define mp make_pair
#define Fi first
#define Se second
#define ALL(v) (v).begin(), (v).end()
#define X real()
#define Y imag()

/* REPmacro */
#define REPS(i, a, n) for (int i = (a); i < (n); ++i)
#define REP(i, n) REPS(i, 0, n)
#define RREP(i, n) REPS(i, 1, n + 1)
#define DEPS(i, a, n) for (int i = (a); i >= n; --i)
#define DEP(i, n) DEPS(i, n, 0)

/* debug */
#define debug(x)                                                               \
  cerr << x << " "                                                             \
       << "(L:" << __LINE__ << ")" << '\n';

/* typedef */
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<vi> vii;
typedef vector<vii> viii;
typedef pair<int, int> pii;
typedef double D;
typedef complex<D> P;

/* const */
const int INF = 999999999;
const int MOD = 1e9 + 7;
const D EPS = 1e-9;
const int dx[] = {0, 1, 0, -1, 1, -1, 1, -1},
          dy[] = {1, 0, -1, 0, 1, -1, -1, 1};

/* func */
inline bool inside(int y, int x, int H, int W) {
  return y >= 0 && x >= 0 && y < H && x < W;
}
inline int in() {
  int x;
  std::cin >> x;
  return x;
}
template <typename T> void print(T x) { std::cout << x << '\n'; }
template <typename T> void print(std::vector<T> &v, string s = " ") {
  REP(i, v.size()) {
    if (i != 0)
      std::cout << s;
    std::cout << v[i];
  }
  std::cout << '\n';
}

/* }}} */

static int n, k;
vector<string> card;
set<string> chie;

signed main() {
  while (cin >> n >> k, n || k) {
    card = vector<string>(n);
    REP(i, n) cin >> card[i];
    sort(ALL(card));
    do {
      string s;
      REP(i, k) s += card[i];
      chie.insert(s);
    } while (next_permutation(ALL(card)));
    print(chie.size());
    // cout << chie.size() << endl;
    chie.clear();
  }

  return 0;
}

Fixed submission:
/* {{{ Shinobu kawaii */
/*
  ______   __        _                  __
.' ____ \ [  |      (_)                [  |
| (___ \_| | |--.   __   _ .--.   .--.  | |.--.   __   _
 _.____`.  | .-. | [  | [ `.-. |/ .'`\ \| '/'`\ \[  | | |
| \____) | | | | |  | |  | | | || \__. ||  \__/ | | \_/ |,
 \______.'[___]|__][___][___||__]'.__.'[__;.__.'  '.__.'_/

*/
/* }}} */

#include <bits/stdc++.h>
using namespace std;

// #define int long long
struct Fast {
  Fast() {
    std::cin.tie(0);
    ios::sync_with_stdio(false);
  }
} fast;

/* cpp template {{{ */

/* short */
#define pb push_back
#define mp make_pair
#define Fi first
#define Se second
#define ALL(v) (v).begin(), (v).end()
#define X real()
#define Y imag()

/* REPmacro */
#define REPS(i, a, n) for (int i = (a); i < (n); ++i)
#define REP(i, n) REPS(i, 0, n)
#define RREP(i, n) REPS(i, 1, n + 1)
#define DEPS(i, a, n) for (int i = (a); i >= n; --i)
#define DEP(i, n) DEPS(i, n, 0)

/* debug */
#define debug(x)                                                               \
  cerr << x << " "                                                             \
       << "(L:" << __LINE__ << ")" << '\n';

/* typedef */
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<vi> vii;
typedef vector<vii> viii;
typedef pair<int, int> pii;
typedef double D;
typedef complex<D> P;

/* const */
const int INF = 999999999;
const int MOD = 1e9 + 7;
const D EPS = 1e-9;
const int dx[] = {0, 1, 0, -1, 1, -1, 1, -1},
          dy[] = {1, 0, -1, 0, 1, -1, -1, 1};

/* func */
inline bool inside(int y, int x, int H, int W) {
  return y >= 0 && x >= 0 && y < H && x < W;
}
inline int in() {
  int x;
  std::cin >> x;
  return x;
}
template <typename T> void print(T x) { std::cout << x << '\n'; }
template <typename T> void print(std::vector<T> &v, string s = " ") {
  REP(i, v.size()) {
    if (i != 0)
      std::cout << s;
    std::cout << v[i];
  }
  std::cout << '\n';
}

/* }}} */

static int n, k;
vector<string> card;
unordered_set<string> chie;

signed main() {
  while (cin >> n >> k, n || k) {
    card = vector<string>(n);
    REP(i, n) cin >> card[i];
    sort(ALL(card));
    do {
      string s;
      REP(i, k) s += card[i];
      chie.insert(s);
    } while (next_permutation(ALL(card)));
    print(chie.size());
    // cout << chie.size() << endl;
    chie.clear();
  }

  return 0;
}