func_code_string: #include <bits/stdc++.h>   using namespace std;   int dp[225][1 << 16];   int dx[4] = {0, -1, 0, 1};   int dy[4] = {1, 0, -1, 0};   int tran[4] = {2, 3, 0, 1};   string s[15];   bool visit[15][15][1 << 16];   int n, m, length, backx, backy, startbody, status;   struct snake {     int x, y, body;   } start;   bool in(int x, int y) { return (x >= 0 && x < n && y >= 0 && y < m); }   bool collision(int x, int y, snake sn) {     int body = sn.body;     int xx = sn.x;     int yy = sn.y;     for (int i = 1; i < length - 1; i++) {       xx += dx[tran[body & 3]];       yy += dy[tran[body & 3]];       body >>= 2;       if (x == xx && y == yy) return true;     }     return false;   }   int BFS() {     queue<pair<snake, int>> Q;     Q.push({start, 0});     visit[start.x][start.y][start.body] = 1;     while (!Q.empty()) {       snake nowsnake = Q.front().first;       int nowstep = Q.front().second;       if (s[nowsnake.x][nowsnake.y] ==  @ ) return nowstep;       Q.pop();       for (int i = 0; i < 4; i++) {         int nextx = nowsnake.x + dx[i];         int nexty = nowsnake.y + dy[i];         if (in(nextx, nexty) && s[nextx][nexty] !=  #  &&             !collision(nextx, nexty, nowsnake)) {           snake nextsnake;           nextsnake.x = nextx;           nextsnake.y = nexty;           nextsnake.body = ((nowsnake.body << 2) & startbody) | i;           if (!visit[nextsnake.x][nextsnake.y][nextsnake.body]) {             visit[nextsnake.x][nextsnake.y][nextsnake.body] = true;             Q.push({nextsnake, nowstep + 1});           }         }       }     }     return -1;   }   int main() {     cin >> n >> m;     for (int i = 0; i < n; i++) cin >> s[i];     length = 0;     for (int i = 0; i < n; i++) {       for (int j = 0; j < m; j++) {         if (s[i][j] !=  #  && s[i][j] !=  @  && s[i][j] !=  . ) {           if (s[i][j] ==  1 ) {             start.x = i;             start.y = j;           }           if (s[i][j] -  0  > length) {             backx = i;             backy = j;             length = s[i][j] -  0 ;           }         }       }     }     startbody = (1 << ((length - 1) * 2)) - 1;     status = 0;     while (s[backx][backy] !=  1 ) {       for (int i = 0; i < 4; i++) {         int newbackx = backx + dx[i];         int newbacky = backy + dy[i];         if (in(newbackx, newbacky) &&             s[newbackx][newbacky] + 1 == s[backx][backy]) {           status <<= 2;           status |= i;           backx = newbackx;           backy = newbacky;           break;         }       }     }     start.body = status;     cout << BFS() << endl;   }   