uva 11624 Fire! 【 BFS 】

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<iostream>
 4 #include<algorithm>
 5 #include<queue>
 6 #include<vector>
 7 using namespace std;
 8 
 9 const int maxn = 1005;
10 const int INF = 1<<30 -1; 
11 int r,c;//r行，c列
12 int d[maxn][maxn];
13 int vis[maxn][maxn];
14 char g[maxn][maxn];
15 int sx,sy;
16 
17 int dir[4][2] = {1,0,-1,0,0,1,0,-1};
18 
19 struct node{
20     int x,y;
21     int step;
22 }p[maxn];
23 
24 queue<node> Q;
25 
26 void bfs1(){
27     memset(vis,0,sizeof(vis));
28     while(!Q.empty()){
29             node v = Q.front();Q.pop();
30             for(int i = 0;i < 4;i++){
31                 int xx = v.x + dir[i][0];
32                 int yy = v.y + dir[i][1];
33                 if(xx < 1 || xx > r || yy < 1 || yy > c || vis[xx][yy] || g[xx][yy] != ‘.‘) continue;
34                 vis[xx][yy] = 1;
35                 d[xx][yy] = min(d[xx][yy],v.step+1);
36                 Q.push(node{xx,yy,v.step+1});
37             }
38     } 
39 }
40 
41 void bfs2(){
42     queue<node> q;
43     memset(vis,0,sizeof(vis));
44     q.push(node{sx,sy,0});vis[sx][sy] = 1;
45     
46     while(!q.empty()){
47         node u = q.front();q.pop();
48         if(u.x == r || u.y == c || u.x == 1 || u.y == 1){
49             printf("%d\n",u.step + 1);
50             return;
51         }
52         for(int i = 0;i < 4;i++){
53             int xx = u.x + dir[i][0];
54             int yy = u.y + dir[i][1];
55             if(xx < 1 || xx > r || yy < 1 || yy > c || vis[xx][yy] || g[xx][yy] != ‘.‘) continue;
56             if(u.step + 1 >= d[xx][yy]) continue;
57             vis[xx][yy] = 1;
58             q.push(node{xx,yy,u.step+1});
59         }
60     }
61     puts("IMPOSSIBLE");
62 }
63 
64 int main(){
65     int T;
66     scanf("%d",&T);
67     while(T--){
68         while(!Q.empty()) Q.pop();
69         scanf("%d %d",&r,&c);
70         for(int i = 1;i <= r;i++){
71             for(int j = 1;j <= c;j++) d[i][j] = INF;
72         }
73         for(int i = 1;i <= r;i++){
74             for(int j = 1;j <= c;j++) {
75                 cin>>g[i][j];
76                 if(g[i][j] == ‘F‘) Q.push(node{i,j,0});
77                 if(g[i][j] == ‘J‘) sx = i,sy = j;
78             }
79         }
80         bfs1();
81         bfs2();
82     }
83     return 0;
84 }