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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define ll long long
  4. #define nmax 1001
  5.  
  6. int n, m;
  7. char a[nmax][nmax];
  8. int monster_dist[nmax][nmax];  // Khoảng cách tối thiểu từ quái vật đến (i, j)
  9. int player_dist[nmax][nmax];   // Khoảng cách từ người chơi đến (i, j)
  10. pair<int, int> parent[nmax][nmax];
  11. char dir[nmax][nmax];          // Hướng di chuyển để đến (i, j)
  12.  
  13. int dx[4] = {1, 0, 0, -1};
  14. int dy[4] = {0, 1, -1, 0};
  15. char moves[4] = {'D', 'R', 'L', 'U'};
  16.  
  17. bool is_valid(int x, int y) {
  18.     return x >= 1 && x <= n && y >= 1 && y <= m && a[x][y] != '#';
  19. }
  20.  
  21. void bfs_monsters(vector<pair<int, int>>& monsters) {
  22.     queue<pair<int, int>> q;
  23.     memset(monster_dist, -1, sizeof(monster_dist));
  24.     for (auto [x, y] : monsters) {
  25.         q.push({x, y});
  26.         monster_dist[x][y] = 0;
  27.     }
  28.     while (!q.empty()) {
  29.         auto [x, y] = q.front(); q.pop();
  30.         for (int i = 0; i < 4; i++) {
  31.             int nx = x + dx[i], ny = y + dy[i];
  32.             if (is_valid(nx, ny) && monster_dist[nx][ny] == -1) {
  33.                 monster_dist[nx][ny] = monster_dist[x][y] + 1;
  34.                 q.push({nx, ny});
  35.             }
  36.         }
  37.     }
  38. }
  39.  
  40. bool bfs_player(int start_x, int start_y) {
  41.     queue<pair<int, int>> q;
  42.     memset(player_dist, -1, sizeof(player_dist));
  43.     q.push({start_x, start_y});
  44.     player_dist[start_x][start_y] = 0;
  45.     while (!q.empty()) {
  46.         auto [x, y] = q.front(); q.pop();
  47.         // Kiểm tra nếu đã đến biên
  48.         if (x == 1 || x == n || y == 1 || y == m) {
  49.             return true;
  50.         }
  51.         for (int i = 0; i < 4; i++) {
  52.             int nx = x + dx[i], ny = y + dy[i];
  53.             if (is_valid(nx, ny) && player_dist[nx][ny] == -1) {
  54.                 // Kiểm tra ô (nx, ny) có an toàn không
  55.                 if (monster_dist[nx][ny] == -1 || player_dist[x][y] + 1 < monster_dist[nx][ny]) {
  56.                     player_dist[nx][ny] = player_dist[x][y] + 1;
  57.                     parent[nx][ny] = {x, y};
  58.                     dir[nx][ny] = moves[i];
  59.                     q.push({nx, ny});
  60.                 }
  61.             }
  62.         }
  63.     }
  64.     return false;
  65. }
  66.  
  67. void solve() {
  68.     cin >> n >> m;
  69.     vector<pair<int, int>> monsters;
  70.     pair<int, int> start;
  71.     for (int i = 1; i <= n; i++) {
  72.         for (int j = 1; j <= m; j++) {
  73.             cin >> a[i][j];
  74.             if (a[i][j] == 'M') monsters.push_back({i, j});
  75.             if (a[i][j] == 'A') start = {i, j};
  76.         }
  77.     }
  78.     // Nếu A ở biên ngay lúc đầu
  79.     if (start.first == 1 || start.first == n || start.second == 1 || start.second == m) {
  80.         cout << "YES\n0\n";
  81.         return;
  82.     }
  83.     bfs_monsters(monsters);
  84.     if (bfs_player(start.first, start.second)) {
  85.         cout << "YES\n";
  86.         // Truy vết đường đi
  87.         vector<char> path;
  88.         int x, y;
  89.         // Tìm điểm biên
  90.         for (x = 1; x <= n; x++) {
  91.             for (y = 1; y <= m; y++) {
  92.                 if ((x == 1 || x == n || y == 1 || y == m) && player_dist[x][y] != -1) {
  93.                     goto reconstruct;
  94.                 }
  95.             }
  96.         }
  97.         reconstruct:
  98.         while (x != start.first || y != start.second) {
  99.             path.push_back(dir[x][y]);
  100.             auto [px, py] = parent[x][y];
  101.             x = px; y = py;
  102.         }
  103.         reverse(path.begin(), path.end());
  104.         cout << path.size() << "\n";
  105.         for (char c : path) cout << c;
  106.     } else {
  107.         cout << "NO";
  108.     }
  109. }
  110.  
  111. int main() {
  112.     solve();
  113.     return 0;
  114. }
Success #stdin #stdout 0.01s 5300KB
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https://ideone.com/d2hmVs
language:
C++ (gcc 8.3)
created:
17 hours ago
visibility:
public

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