poj 2251

    最短路径一定要用BFS,
DFS求最短路径不及BFS系列

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1. #include <iostream>
   
2. #include <stdio.h>
   
3. #include <cstring>
   
4. #include <queue>
   
5. 
   
6. using namespace std;
   
7. 
   
8. #define MAX_V (40+1)
   
9. struct point{
   
10.     int x;
    
11.     int y;
    
12.     int z;
    
13.     int l;
    
14. };
    
15. 
    
16. char T[MAX_V][MAX_V][MAX_V];
    
17. char V[MAX_V][MAX_V][MAX_V];
    
18. 
    
19. int l,r,c;
    
20. int si,sj,sk;
    
21. 
    
22. struct move{
    
23.     int x;
    
24.     int y;
    
25.     int z;
    
26. }MOVE[]={ {-1,0,0},{1,0,0},{0,-1,0},{0,1,0},{0,0,-1},{0,0,1} };
    
27. 
    
28. int ml = sizeof(MOVE) /sizeof(move);
    
29. 
    
30. int bfs()
    
31. {
    
32.     
    
33.     struct point Q[50000];
    
34.     Q[0].x=si;
    
35.     Q[0].y=sj;
    
36.     Q[0].z=sk;
    
37.     Q[0].l=1;    
    
38.     int h=0,t=1;
    
39. 
    
40.     memset(V,0,sizeof(V));
    
41.     V[si][sj][sk]=1;
    
42. 
    
43.     while(h<t)
    
44.     {
    
45.         //point p=Q.front();
    
46.         //Q.pop();
    
47.         point p=Q[h];
    
48.         h++;
    
49.         //printf("(%d,%d,%d)=%d\n",p.x,p.y,p.z,p.l);
    
50.         //V[x][y][z]=1; //习惯性的再这里加访问标志
            //如果不是求最小生成树等BFS变种，其实一个元素放到队列里，就是已经访问了。
    
51.         for(int m=0;m<ml;m++)
    
52.         {
    
53.             int x=MOVE[m].x + p.x;
    
54.             int y=MOVE[m].y + p.y;
    
55.             int z=MOVE[m].z + p.z;
    
56. 
    
57.             if( x < 1 || y < 1 || z < 1)
    
58.                 continue;
    
59. 
    
60.             if(x > l || y > r || z > c)
    
61.                 continue;
    
62. 
    
63.             if(V[x][y][z] != 0)
    
64.                 continue;
    
65. 
    
66.             if(T[x][y][z] == 'E')
    
67.                 return p.l;    
    
68. 
    
69.             if(T[x][y][z] == '.')
    
70.             {
    
71.                 Q[t].x=x;
    
72.                 Q[t].y=y;
    
73.                 Q[t].z=z;
    
74.                 Q[t].l=p.l+1;    
    
75.                 t++;
    
76.                 V[x][y][z]=1;  //所以BFS的visit应该放在这里设标志。这样可以减少很多出队入队操作，也避免重复
    
77.             }
    
78.         }
    
79.         
    
80.     }
    
81. 
    
82.     return -1;
    
83. }
    
84. int main()
    
85. {
    
86.     while(cin>>l>>r>>c)
    
87.     {
    
88.         if(l <= 0)
    
89.             return 0;
    
90.         for(int i=1;i<=l;i++)
    
91.         {
    
92.             for(int j=1;j<=r;j++)
    
93.             {
    
94.                 for(int k=1;k<=c;k++)
    
95.                 {
    
96.                     char c;
    
97.                     cin>>c;
    
98.                     T[i][j][k]=c;
    
99.                     //printf("read (%d,%d,%d)=%c\n",i,j,k,(char)T[i][j][k]);
    
100.                     if( T[i][j][k] == 'S')
     
101.                     {
     
102.                         si=i;
     
103.                         sj=j;
     
104.                         sk=k;
     
105.                     }
     
106.                 }
     
107.             }
     
108.         }
     
109. 
     
110.         int ret = bfs();
     
111.         if(ret < 0)
     
112.             cout<<"Trapped!"<<endl;
     
113.         else
     
114.             cout<<"Escaped in "<<ret<<" minute(s)."<<endl;
     
115.     }
     
116. }

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