Problem p00750 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <algorithm>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <memory>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;

#if __GNUC__
#include <tr1/unordered_map>
#include <tr1/unordered_set>
using namespace tr1;
#else
#include <unordered_map>
#include <unordered_set>
#endif

#ifdef _MSC_VER
#define __typeof__ decltype
template <class T> int popcount(T n) {
  return n ? 1 + popcount(n & (n - 1)) : 0;
}
#endif
#ifdef __GNUC__
template <class T> int popcount(T n);
template <> int popcount(unsigned int n) { return __builtin_popcount(n); }
template <> int popcount(int n) { return __builtin_popcount(n); }
template <> int popcount(unsigned long long n) {
  return __builtin_popcountll(n);
}
template <> int popcount(long long n) { return __builtin_popcountll(n); }
#endif

#define rep (i, n) for (int i = 0; i < (int)n; ++i)
#define foreach(it, c)                                                         \\
  for (__typeof__((c).begin()) it = (c).begin(); it != (c).end(); ++it)
#define rforeach(it, c)                                                        \\
  for (__typeof__((c).rbegin()) it = (c).rbegin(); it != (c).rend(); ++it)
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define CL(arr, val) memset(arr, val, sizeof(arr))
#define MEMCPY(dest, src) memcpy(dest, src, sizeof(src))

template <class T> void max_swap(T &a, const T &b) { a = max(a, b); }
template <class T> void min_swap(T &a, const T &b) { a = min(a, b); }

typedef long long ll;
typedef pair<int, int> pint;

template <class T> string to_s(const T &a) {
  ostringstream os;
  os << a;
  return os.str();
}

const double EPS = 1e-8;
const double PI = acos(-1.0);
const int dx[] = {0, 1, 0, -1};
const int dy[] = {1, 0, -1, 0};
bool valid_pos(int x, int y, int w, int h) {
  return 0 <= x && x < w && 0 <= y && y < h;
}

template <class T>
void print(T a, int n, int br = 1, const string &deli = ", ") {
  cout << "{ ";
  for (int i = 0; i < n; ++i) {
    cout << a[i];
    if (i + 1 != n)
      cout << deli;
  }
  cout << " }";
  while (br--)
    cout << endl;
}
template <class T>
void print(const vector<T> &v, int br = 1, const string &deli = ", ") {
  print(v, v.size(), br, deli);
}
template <class T> void print2d(T a, int w, int h, int width = -1, int br = 1) {
  for (int i = 0; i < h; ++i) {
    for (int j = 0; j < w; ++j) {
      if (width != -1)
        cout.width(width);
      cout << a[i][j] << ' ';
    }
    cout << endl;
  }
  while (br--)
    cout << endl;
}

template <class T> void input(int n, T &a) {
  for (int i = 0; i < n; ++i)
    cin >> a[i];
}
template <class T, class U> void input(int n, T &a, U &b) {
  for (int i = 0; i < n; ++i)
    cin >> a[i] >> b[i];
}
template <class T, class U, class V> void input(int n, T &a, U &b, V &c) {
  for (int i = 0; i < n; ++i)
    cin >> a[i] >> b[i] >> c[i];
}
template <class T> vector<T> input(int n) {
  vector<T> res(n);
  for (int i = 0; i < n; ++i)
    cin >> res[i];
  return res;
}

int n, a, s, g;
string solve() {
  typedef pair<string, int> P;
  vector<P> e[40];
  for (int i = 0; i < a; ++i) {
    int x, y;
    string t;
    cin >> x >> y >> t;
    e[x].push_back(P(t, y));
  }

  const string INF = string(1, 'z' + 1);
  int max_len = n * 6 * 2;
  string dis[42][40 * 6 * 2 + 6];
  for (int i = 0; i < n; ++i)
    for (int j = 0; j <= max_len; ++j)
      dis[i][j] = INF;

  priority_queue<P, vector<P>, greater<P>> q;
  q.push(P("", s));
  dis[s][0] = "";
  while (!q.empty()) {
    string t = q.top().first;
    int p = q.top().second;
    q.pop();
    if (t > dis[p][t.size()])
      continue;

    foreach (it, e[p]) {
      int to = it->second;
      string nt = t + it->first;
      if (nt.size() <= max_len && nt < dis[to][nt.size()]) {
        dis[to][nt.size()] = nt;
        q.push(P(nt, to));
      }
    }
  }

  string res = INF;
  for (int i = 0; i <= max_len; ++i)
    min_swap(res, dis[g][i]);

  if (res == INF || res.size() > 6 * (n - 1))
    return "NO";
  else
    return res;
}
int main() {
  ios::sync_with_stdio(false);

  while (cin >> n >> a >> s >> g, n)
    cout << solve() << endl;
}

Error: TLE

Fixed submission:

#include <algorithm>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <memory>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;

#if __GNUC__
#include <tr1/unordered_map>
#include <tr1/unordered_set>
using namespace tr1;
#else
#include <unordered_map>
#include <unordered_set>
#endif

#ifdef _MSC_VER
#define __typeof__ decltype
template <class T> int popcount(T n) {
  return n ? 1 + popcount(n & (n - 1)) : 0;
}
#endif
#ifdef __GNUC__
template <class T> int popcount(T n);
template <> int popcount(unsigned int n) { return __builtin_popcount(n); }
template <> int popcount(int n) { return __builtin_popcount(n); }
template <> int popcount(unsigned long long n) {
  return __builtin_popcountll(n);
}
template <> int popcount(long long n) { return __builtin_popcountll(n); }
#endif

#define rep (i, n) for (int i = 0; i < (int)n; ++i)
#define foreach(it, c)                                                         \\
  for (__typeof__((c).begin()) it = (c).begin(); it != (c).end(); ++it)
#define rforeach(it, c)                                                        \\
  for (__typeof__((c).rbegin()) it = (c).rbegin(); it != (c).rend(); ++it)
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define CL(arr, val) memset(arr, val, sizeof(arr))
#define MEMCPY(dest, src) memcpy(dest, src, sizeof(src))

template <class T> void max_swap(T &a, const T &b) { a = max(a, b); }
template <class T> void min_swap(T &a, const T &b) { a = min(a, b); }

typedef long long ll;
typedef pair<int, int> pint;

template <class T> string to_s(const T &a) {
  ostringstream os;
  os << a;
  return os.str();
}

const double EPS = 1e-8;
const double PI = acos(-1.0);
const int dx[] = {0, 1, 0, -1};
const int dy[] = {1, 0, -1, 0};
bool valid_pos(int x, int y, int w, int h) {
  return 0 <= x && x < w && 0 <= y && y < h;
}

template <class T>
void print(T a, int n, int br = 1, const string &deli = ", ") {
  cout << "{ ";
  for (int i = 0; i < n; ++i) {
    cout << a[i];
    if (i + 1 != n)
      cout << deli;
  }
  cout << " }";
  while (br--)
    cout << endl;
}
template <class T>
void print(const vector<T> &v, int br = 1, const string &deli = ", ") {
  print(v, v.size(), br, deli);
}
template <class T> void print2d(T a, int w, int h, int width = -1, int br = 1) {
  for (int i = 0; i < h; ++i) {
    for (int j = 0; j < w; ++j) {
      if (width != -1)
        cout.width(width);
      cout << a[i][j] << ' ';
    }
    cout << endl;
  }
  while (br--)
    cout << endl;
}

template <class T> void input(int n, T &a) {
  for (int i = 0; i < n; ++i)
    cin >> a[i];
}
template <class T, class U> void input(int n, T &a, U &b) {
  for (int i = 0; i < n; ++i)
    cin >> a[i] >> b[i];
}
template <class T, class U, class V> void input(int n, T &a, U &b, V &c) {
  for (int i = 0; i < n; ++i)
    cin >> a[i] >> b[i] >> c[i];
}
template <class T> vector<T> input(int n) {
  vector<T> res(n);
  for (int i = 0; i < n; ++i)
    cin >> res[i];
  return res;
}

int n, a, s, g;
int x[432], y[432];
string lab[432];
string solve() {
  const string INF = string(1, 'z' + 1);
  string dis[42][40 * 6 + 6];
  for (int i = 0; i < n; ++i)
    for (int j = 0; j < 40 * 6; ++j)
      dis[i][j] = INF;

  string res = INF;
  dis[s][0] = "";
  for (int C = 0;; ++C) {
    bool updated = false;
    for (int i = 0; i < a; ++i) {
      for (int j = 0; j < n * 6; ++j) {
        string t = dis[x[i]][j] + lab[i];
        string &d = dis[y[i]][t.size()];
        if (t < d) {
          if (y[i] == g) {
            if (t.size() >= n * 6 && t < res)
              return "NO";
            else
              min_swap(res, t);
          }

          updated = true;
          d = t;
        }
      }
    }
    if (!updated)
      break;
  }

  if (res == INF)
    return "NO";
  else
    return res;
}
int main() {
  ios::sync_with_stdio(false);

  while (cin >> n >> a >> s >> g, n) {
    input(a, x, y, lab);
    cout << solve() << endl;
  }
}