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 }