UVa 11624 - Fire!

题目链接：http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=24&page=show_problem&problem=2671

分析：广搜，在加入Joe的起始位置之前，先把所有着火点加入队列。Joe只能到达没有障碍和火势控制的格子。

  1 #include <cstdio>
  2 #include <cstring>
  3 
  4 const int MAXN = 1004;
  5 const int dx[] = { -1, 1, 0, 0 };
  6 const int dy[] = { 0, 0, -1, 1 };
  7 
  8 struct point
  9 {
 10     int x, y;
 11     int minit;
 12     bool fir;
 13 };
 14 
 15 char map[MAXN][MAXN];
 16 bool vis[MAXN][MAXN];
 17 point Q[MAXN * MAXN];
 18 point start;
 19 point fire[MAXN * MAXN];
 20 int r, c;
 21 int cnt;
 22 
 23 bool check( int x, int y )
 24 {
 25     return  x > 0 && x <= r && y > 0 && y <= c ;
 26 }
 27 
 28 int BFS()
 29 {
 30     int front = 0, rear = 0;
 31 
 32     for ( int i = 0; i < cnt; ++i )
 33         Q[ rear++ ] = fire[i];
 34 
 35     Q[ rear++ ] = start;
 36 
 37     while ( front < rear )
 38     {
 39         point &tp = Q[front];
 40 
 41         if ( tp.fir )
 42         {
 43             for ( int i = 0; i < 4; ++i )
 44             {
 45                 int xx = tp.x + dx[i];
 46                 int yy = tp.y + dy[i];
 47                 if ( check(xx, yy) && ( !vis[xx][yy] ) )
 48                 {
 49                     vis[xx][yy] = true;
 50                     Q[rear].fir = true;
 51                     Q[rear].minit = tp.minit + 1;
 52                     Q[rear].x = xx;
 53                     Q[rear++].y = yy;
 54                 }
 55             }
 56         }
 57         else if ( map[ tp.x ][ tp.y ] == 'J' )
 58         {
 59             for ( int i = 0; i < 4; ++i )
 60             {
 61                 int xx = tp.x + dx[i];
 62                 int yy = tp.y + dy[i];
 63                 if ( !vis[xx][yy] )
 64                 {
 65                     vis[xx][yy] = true;
 66                     map[xx][yy] = 'J';
 67                     Q[rear].fir = false;
 68                     Q[rear].minit = tp.minit + 1;
 69                     Q[rear].x = xx;
 70                     Q[rear].y = yy;
 71                     if ( !check( xx, yy ) ) return Q[rear].minit;
 72                     ++rear;
 73                 }
 74             }
 75         }
 76 
 77             ++front;
 78     }
 79 
 80     return -1;
 81 }
 82 
 83 int main()
 84 {
 85     int T;
 86     scanf( "%d", &T );
 87     while ( T-- )
 88     {
 89         scanf( "%d%d", &r, &c );
 90 
 91         cnt = 0;
 92         memset( vis, false, sizeof(vis) );
 93         memset( map, '.', sizeof(map) );
 94 
 95         for ( int i = 1; i <= r; ++i )
 96         {
 97             getchar();
 98             for ( int j = 1; j <= c; ++j )
 99             {
100                 map[i][j] = getchar();
101                 switch( map[i][j] )
102                 {
103                 case 'J':
104                     start.x = i;
105                     start.y = j;
106                     start.minit = 0;
107                     start.fir = false;
108                     vis[i][j] = true;
109                     break;
110 
111                 case 'F':
112                     vis[i][j] = true;
113                     fire[cnt].x = i;
114                     fire[cnt].y = j;
115                     fire[cnt].fir = true;
116                     fire[ cnt++ ].minit = 0;
117                     break;
118 
119                 case '#':
120                     vis[i][j] = true;
121                     break;
122                 }
123             }
124         }
125         int ans = BFS();
126         if ( ans == -1 ) puts("IMPOSSIBLE");
127         else printf( "%d\n", ans );
128     }
129     return 0;
130 }

 

posted @ 2012-12-05 17:24  冰鸮  阅读(406)  评论(0)  编辑  收藏  举报