BFS。wa了一下午，原来是YES，写成了Yes。
1 #include <iostream> 2 #include <cstdio> 3 #include <cstring> 4 #include <queue> 5 using namespace std; 6 7 typedef struct node_st{ 8 int x, y; 9 int dir; 10 int turn; 11 node_st() {} 12 node_st(int xx, int yy, int ddir, int tturn) { 13 x = xx; y = yy; dir = ddir; turn = tturn; 14 } 15 } node_st; 16 17 int map[1005][1005]; 18 int n, m; 19 int dirs[4][2] = {{0,1},{0,-1},{1,0},{-1,0}}; 20 char turns[1005][1005]; 21 22 bool bfs(int bx, int by, int ex, int ey) { 23 queue<node_st> que; 24 bool val = false; 25 node_st node; 26 int x, y, dir, turn; 27 28 memset(turns, 0, sizeof(turns)); 29 turns[bx][by] = 1; 30 que.push(node_st(bx, by, -1, 0)); 31 32 while ( !que.empty() ) { 33 node = que.front(); 34 //printf("x=%d, y=%d, dir=%d, turn=%d ", node.x, node.y, node.dir, node.turn); 35 if (node.x == ex && node.y == ey) { 36 val = true; 37 break; 38 } 39 que.pop(); 40 for (int i=0; i<4; ++i) { 41 x = node.x + dirs[i][0]; 42 y = node.y + dirs[i][1]; 43 dir = i; 44 turn = node.turn; 45 if (x<1 || x>n || y<1 || y>m) 46 continue; 47 if (map[x][y] && (x!=ex || y!=ey)) 48 continue; 49 if (dir!=node.dir && node.dir!=-1) 50 ++turn; 51 //printf(" x=%d, y=%d, dir=%d, turn=%d ", x, y, dir, turn); 52 if (turn > 2) 53 continue; 54 if (turns[x][y]==0 || turn+1 <= turns[x][y]) { 55 turns[x][y] = turn+1; 56 que.push(node_st(x, y, dir, turn)); 57 } 58 } 59 } 60 61 return val; 62 } 63 64 int main() { 65 int q, x1, x2, y1, y2; 66 int i, j; 67 68 while (scanf("%d %d", &n, &m)!=EOF && (n||m)) { 69 for (i=1; i<=n; ++i) 70 for (j=1; j<=m; ++j) 71 scanf("%d", &map[i][j]); 72 scanf("%d", &q); 73 while (q--) { 74 scanf("%d %d %d %d", &x1, &y1, &x2, &y2); 75 if (x1==x2 && y1==y2) { 76 printf("NO "); 77 continue; 78 } 79 if (map[x1][y1]!=map[x2][y2] || map[x1][y1]==0 || map[x2][y2]==0) { 80 printf("NO "); 81 continue; 82 } 83 if ( bfs(x1, y1, x2, y2) ) 84 printf("YES "); 85 else 86 printf("NO "); 87 } 88 } 89 90 return 0; 91 }