func_code_string: #include <bits/stdc++.h>   using namespace std;   char field[50][50];   bool used[50][50];   int n, m, k;   int counts[26];   int cur_set;   set<string> min_ways;   int min_len = INT_MAX;   int start_x, start_y, end_x, end_y;   vector<char> alpha(0);   bool comp(pair<int, int> a, pair<int, int> b) {     if (field[a.first][a.second] ==  T ) return true;     if (field[b.first][b.second] ==  T ) return false;     return field[a.first][a.second] < field[b.first][b.second];   }   vector<pair<int, int>> find_near(int from_y, int from_x,                                    const set<char> &from_set) {     vector<pair<int, int>> near(0);     if (from_y > 0 && !used[from_y - 1][from_x] &&         from_set.find(field[from_y - 1][from_x]) != from_set.end())       near.push_back(make_pair(from_y - 1, from_x));     if (from_y < n - 1 && !used[from_y + 1][from_x] &&         from_set.find(field[from_y + 1][from_x]) != from_set.end())       near.push_back(make_pair(from_y + 1, from_x));     if (from_x > 0 && !used[from_y][from_x - 1] &&         from_set.find(field[from_y][from_x - 1]) != from_set.end())       near.push_back(make_pair(from_y, from_x - 1));     if (from_x < m - 1 && !used[from_y][from_x + 1] &&         from_set.find(field[from_y][from_x + 1]) != from_set.end())       near.push_back(make_pair(from_y, from_x + 1));     sort(near.begin(), near.end(), comp);     return near;   }   set<char> find_set_near(int from_y, int from_x) {     set<char> near = set<char>();     if (from_y > 0 && !used[from_y - 1][from_x])       near.insert(field[from_y - 1][from_x]);     if (from_y < n - 1 && !used[from_y + 1][from_x])       near.insert(field[from_y + 1][from_x]);     if (from_x > 0 && !used[from_y][from_x - 1])       near.insert(field[from_y][from_x - 1]);     if (from_x < m - 1 && !used[from_y][from_x + 1])       near.insert(field[from_y][from_x + 1]);     near.erase( T );     near.erase( S );     return near;   }   set<char> find_second_near_set(int from_y, int from_x, set<char> &not_from) {     bool l2, l1, r1, r2, u1, u2, d1, d2;     l2 = from_x - 2 >= 0;     l1 = from_x > 0;     r1 = from_x + 2 < m;     r2 = from_x + 1 < m;     u2 = from_y - 2 >= 0;     u1 = from_y > 0;     d1 = from_y + 1 < n;     d2 = from_y + 2 < n;     int yu2 = from_y - 2;     int yu1 = from_y - 1;     int yd1 = from_y + 1;     int yd2 = from_y + 2;     int xl2 = from_x - 2;     int xl1 = from_x - 1;     int xr1 = from_x + 1;     int xr2 = from_x + 2;     set<char> ret = set<char>();     if (l1 && u2) ret.insert(field[yu2][xl1]);     if (u2) ret.insert(field[yu2][from_x]);     if (u2 && r1) ret.insert(field[yu2][xr1]);     if (r2) {       if (u1) ret.insert(field[yu1][xr2]);       ret.insert(field[from_y][xr2]);       if (d1) ret.insert(field[yd1][xr2]);     }     if (d2) {       if (r1) ret.insert(field[yd2][xr1]);       ret.insert(field[yd2][from_x]);       if (l1) ret.insert(field[yd2][xl1]);     }     if (l2) {       if (d1) ret.insert(field[yd1][xl2]);       ret.insert(field[from_y][xl2]);       if (u1) ret.insert(field[yu1][xl2]);     }     for (set<char>::iterator i = not_from.begin(); i != not_from.end(); i++)       ret.erase(*i);     return ret;   }   void read() {     set<char> set_alpha = set<char>();     cin >> n >> m >> k;     for (int i = 0; i < n; i++)       for (int j = 0; j < m; j++) {         cin >> field[i][j];         if (field[i][j] ==  S ) {           start_y = i;           start_x = j;         } else if (field[i][j] ==  T ) {           end_y = i;           end_x = j;         } else           set_alpha.insert(field[i][j]);       }     for (set<char>::iterator i = set_alpha.begin(); i != set_alpha.end(); i++)       alpha.push_back(*i);   }   struct cell {     pair<int, int> pos;     string s;   };   struct comp2 {     bool operator()(const cell &a, const cell &b) {       if (a.s.size() != b.s.size())         return a.s.size() < b.s.size();       else         return a.s < b.s;     }   };   set<set<char>> last_sets;   bool wave(set<char> &cur_set) {     if (last_sets.find(cur_set) != last_sets.end())       return false;     else       last_sets.insert(cur_set);     memset(used, false, 2500);     used[start_y][start_x] = true;     cur_set.insert( T );     multiset<cell, comp2> myque;     cell tmp;     tmp.pos = make_pair(start_y, start_x);     tmp.s = string(  );     myque.insert(tmp);     while (!myque.empty()) {       cell cur_cell = *myque.begin();       myque.erase(myque.begin());       if (cur_cell.s.length() > min_len) break;       vector<pair<int, int>> near =           find_near(cur_cell.pos.first, cur_cell.pos.second, cur_set);       for (vector<pair<int, int>>::iterator i = near.begin(); i != near.end();            i++) {         if (field[i->first][i->second] ==  T ) {           if (cur_cell.s.length() < min_len) {             min_ways.clear();             min_len = cur_cell.s.length();           }           min_ways.insert(cur_cell.s);           break;         }         used[i->first][i->second] = true;         cell tmp = cur_cell;         tmp.pos = *i;         tmp.s.push_back(field[i->first][i->second]);         myque.insert(tmp);       }     }     cur_set.erase( T );     return false;   }   int main() {     read();     string s(  );     set<char> start_set = find_set_near(start_y, start_x);     set<char> end_set = find_set_near(end_y, end_x);     int l = alpha.size();     set<char> cur_set = set<char>();     if (!l)       wave(cur_set);     else {       for (set<char>::iterator a = start_set.begin(); a != start_set.end(); a++) {         cur_set.insert(*a);         if (cur_set.size() == k || l < k && cur_set.size() == l)           wave(cur_set);         else {           for (set<char>::iterator b = end_set.begin(); b != end_set.end(); b++) {             cur_set.insert(*b);             if (cur_set.size() == k || l < k && cur_set.size() == l)               wave(cur_set);             else {               for (int i = 0; i < l; i++) {                 if (cur_set.end() != cur_set.find(alpha[i])) continue;                 cur_set.insert(alpha[i]);                 if (cur_set.size() == k || l < k && cur_set.size() == l)                   wave(cur_set);                 else {                   for (int j = i + 1; j < l; j++) {                     if (cur_set.end() != cur_set.find(alpha[j])) continue;                     cur_set.insert(alpha[j]);                     if ((*a) == (*b) && cur_set.size() < k) {                       set<char> second_set =                           find_second_near_set(start_y, start_x, cur_set);                       if (!second_set.size())                         wave(cur_set);                       else {                         for (set<char>::iterator p = second_set.begin();                              p != second_set.end(); p++) {                           cur_set.insert(*p);                           wave(cur_set);                           cur_set.erase(*p);                         }                       }                     } else                       wave(cur_set);                     cur_set.erase(alpha[j]);                   }                 }                 cur_set.erase(alpha[i]);               }             }             cur_set.erase(*b);           }         }         cur_set.erase(*a);       }     }   label_end:     if (min_len == INT_MAX)       cout <<  -1 ;     else       cout << (*min_ways.begin());   }   