Problem p00839 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <algorithm>
#include <bitset>
#include <cfloat>
#include <climits>
#include <cmath>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
using namespace std;

int n;
vector<vector<int>> to;

void solve(vector<string> start, map<vector<string>, int> &history) {
  queue<vector<string>> q1;
  q1.push(start);
  history[start] = 0;

  for (int a = 1; a <= 3; ++a) {
    queue<vector<string>> q2;
    while (!q1.empty()) {
      vector<string> s = q1.front();
      q1.pop();

      for (int i = 0; i < n * 2; ++i) {
        for (unsigned j = 0; j < to[i].size(); ++j) {
          vector<string> t = s;
          while (!t[i / 2].empty()) {
            char c;
            if (i % 2 == 0) {
              c = t[i / 2][0];
              t[i / 2] = t[i / 2].substr(1);
            } else {
              c = t[i / 2][t[i / 2].size() - 1];
              t[i / 2] = t[i / 2].substr(0, t[i / 2].size() - 1);
            }

            if (to[i][j] % 2 == 0) {
              t[to[i][j] / 2] = c + t[to[i][j] / 2];
            } else {
              t[to[i][j] / 2] += c;
            }

            if (history.find(t) == history.end()) {
              q2.push(t);
              history[t] = a;
            }
          }
        }
      }
    }
    q1 = q2;
  }
}

int main() {
  for (;;) {
    int m;
    cin >> n >> m;
    if (n == 0)
      return 0;

    to.assign(2 * n, vector<int>());
    for (int i = 0; i < m; ++i) {
      string s, t;
      cin >> s >> t;
      int a = (s[0] - '0') * 2;
      int b = (t[0] - '0') * 2;
      if (s[1] == 'E')
        ++a;
      if (t[1] == 'E')
        ++b;
      to[a].push_back(b);
      to[b].push_back(a);
    }

    vector<string> s(n), t(n);
    for (int i = 0; i < n; ++i) {
      cin >> s[i];
      if (s[i] == "-")
        s[i] = "";
    }
    for (int i = 0; i < n; ++i) {
      cin >> t[i];
      if (t[i] == "-")
        t[i] = "";
    }

    map<vector<string>, int> history1, history2;
    solve(t, history2);
    solve(s, history1);

    int ret = INT_MAX;
    map<vector<string>, int>::iterator it1, it2;
    it1 = history1.begin();
    it2 = history2.begin();
    while (it1 != history1.end() && it2 != history2.end()) {
      if (it1->first == it2->first)
        ret = min(ret, it1->second + it2->second);
      if (it1->first < it2->first)
        ++it1;
      else
        ++it2;
    }

    cout << ret << endl;
  }
}

Error: TLE

Fixed submission:

#include <algorithm>
#include <bitset>
#include <cfloat>
#include <climits>
#include <cmath>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
using namespace std;

int n;
vector<vector<int>> to;

void solve(vector<string> start, map<vector<string>, int> &history) {
  queue<vector<string>> q1;
  q1.push(start);
  history[start] = 0;

  for (int a = 1; a <= 3; ++a) {
    queue<vector<string>> q2;
    while (!q1.empty()) {
      vector<string> s = q1.front();
      q1.pop();

      for (int i = 0; i < n * 2; ++i) {
        for (unsigned j = 0; j < to[i].size(); ++j) {
          vector<string> t = s;
          while (!t[i / 2].empty()) {
            char c;
            if (i % 2 == 0) {
              c = t[i / 2][0];
              t[i / 2] = t[i / 2].substr(1);
            } else {
              c = t[i / 2][t[i / 2].size() - 1];
              t[i / 2] = t[i / 2].substr(0, t[i / 2].size() - 1);
            }

            if (to[i][j] % 2 == 0) {
              t[to[i][j] / 2] = c + t[to[i][j] / 2];
            } else {
              t[to[i][j] / 2] += c;
            }

            if (history.find(t) == history.end()) {
              q2.push(t);
              history[t] = a;
            }
          }
        }
      }
    }
    q1 = q2;
  }
}

int main() {
  for (;;) {
    int m;
    cin >> n >> m;
    if (n == 0)
      return 0;

    to.resize(2 * n);
    for (int i = 0; i < m; ++i) {
      string s, t;
      cin >> s >> t;
      int a = (s[0] - '0') * 2;
      int b = (t[0] - '0') * 2;
      if (s[1] == 'E')
        ++a;
      if (t[1] == 'E')
        ++b;
      to[a].push_back(b);
      to[b].push_back(a);
    }

    vector<string> s(n), t(n);
    for (int i = 0; i < n; ++i) {
      cin >> s[i];
      if (s[i] == "-")
        s[i] = "";
    }
    for (int i = 0; i < n; ++i) {
      cin >> t[i];
      if (t[i] == "-")
        t[i] = "";
    }

    map<vector<string>, int> history1, history2;
    solve(t, history2);
    solve(s, history1);

    int ret = INT_MAX;
    map<vector<string>, int>::iterator it1, it2;
    it1 = history1.begin();
    it2 = history2.begin();
    while (it1 != history1.end() && it2 != history2.end()) {
      if (it1->first == it2->first)
        ret = min(ret, it1->second + it2->second);
      if (it1->first < it2->first)
        ++it1;
      else
        ++it2;
    }

    cout << ret << endl;
  }
}