状态压缩+BFS，一次AC。
1 /* 1885 */ 2 #include <iostream> 3 #include <queue> 4 #include <cstring> 5 #include <cstdio> 6 #include <cstdlib> 7 using namespace std; 8 9 #define MAXN 105 10 11 bool visit[MAXN][MAXN][16]; 12 13 typedef struct node_t { 14 int x, y, t, k; 15 node_t() {} 16 node_t(int xx, int yy, int tt, int kk) { 17 x = xx; y = yy; t = tt; k = kk; 18 } 19 } node_t; 20 21 int n, m; 22 node_t beg; 23 char map[MAXN][MAXN]; 24 int dir[4][2] = { 25 -1,0,1,0,0,-1,0,1 26 }; 27 28 inline bool check(int x, int y) { 29 return x<0 || x>=n || y<0 || y>=m; 30 } 31 32 int bfs() { 33 int i, j, k; 34 int x, y, t; 35 node_t nd; 36 queue<node_t> Q; 37 38 memset(visit, false, sizeof(visit)); 39 visit[beg.x][beg.y][beg.k] = true; 40 Q.push(beg); 41 42 while (!Q.empty()) { 43 nd = Q.front(); 44 Q.pop(); 45 t = nd.t + 1; 46 for (i=0; i<4; ++i) { 47 x = nd.x + dir[i][0]; 48 y = nd.y + dir[i][1]; 49 if (check(x, y) || map[x][y]=='#') 50 continue; 51 if (map[x][y] == 'X') 52 return t; 53 k = nd.k; 54 if (map[x][y]>='A' && map[x][y]<='D') { 55 j = map[x][y] - 'A'; 56 if ((nd.k & (1<<j)) == 0) 57 continue; 58 } else if (map[x][y]>='a' && map[x][y]<='d') { 59 j = map[x][y] - 'a'; 60 k |= (1<<j); 61 } 62 if (visit[x][y][k]) 63 continue; 64 visit[x][y][k] = true; 65 Q.push(node_t(x, y, t, k)); 66 } 67 } 68 69 return -1; 70 } 71 72 int main() { 73 int i, j, k; 74 75 #ifndef ONLINE_JUDGE 76 freopen("data.in", "r", stdin); 77 freopen("data.out", "w", stdout); 78 #endif 79 80 beg.k = beg.t = 0; 81 while (scanf("%d%d",&n,&m)!=EOF && (n||m)) { 82 for (i=0; i<n; ++i) { 83 scanf("%s", map[i]); 84 for (j=0; j<m; ++j) { 85 if (map[i][j] == '*') { 86 beg.x = i; 87 beg.y = j; 88 } else if (map[i][j] == 'Y') { 89 map[i][j] = 'A'; 90 } else if (map[i][j] == 'R') { 91 map[i][j] = 'C'; 92 } else if (map[i][j] == 'G') { 93 map[i][j] = 'D'; 94 } else if (map[i][j] == 'y') { 95 map[i][j] = 'a'; 96 } else if (map[i][j] == 'r') { 97 map[i][j] = 'c'; 98 } else if (map[i][j] == 'g') { 99 map[i][j] = 'd'; 100 } 101 } 102 } 103 k = bfs(); 104 if (k < 0) 105 puts("The poor student is trapped!"); 106 else 107 printf("Escape possible in %d steps. ", k); 108 } 109 110 return 0; 111 }