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。

#include <cstdio>
#include <cstring>

const int MAXN = 1004;
const int dx[] = { -1, 1, 0, 0 };
const int dy[] = { 0, 0, -1, 1 };

struct point
{
    int x, y;
    int minit;
    bool fir;
};

char map[MAXN][MAXN];
bool vis[MAXN][MAXN];
point Q[MAXN * MAXN];
point start;
point fire[MAXN * MAXN];
int r, c;
int cnt;

bool check( int x, int y )
{
    return  x > 0 && x <= r && y > 0 && y <= c ;
}

int BFS()
{
    int front = 0, rear = 0;

    for ( int i = 0; i < cnt; ++i )
        Q[ rear++ ] = fire[i];

    Q[ rear++ ] = start;

    while ( front < rear )
    {
        point &tp = Q[front];

        if ( tp.fir )
        {
            for ( int i = 0; i < 4; ++i )
            {
                int xx = tp.x + dx[i];
                int yy = tp.y + dy[i];
                if ( check(xx, yy) && ( !vis[xx][yy] ) )
                {
                    vis[xx][yy] = true;
                    Q[rear].fir = true;
                    Q[rear].minit = tp.minit + 1;
                    Q[rear].x = xx;
                    Q[rear++].y = yy;
                }
            }
        }
        else if ( map[ tp.x ][ tp.y ] == 'J' )
        {
            for ( int i = 0; i < 4; ++i )
            {
                int xx = tp.x + dx[i];
                int yy = tp.y + dy[i];
                if ( !vis[xx][yy] )
                {
                    vis[xx][yy] = true;
                    map[xx][yy] = 'J';
                    Q[rear].fir = false;
                    Q[rear].minit = tp.minit + 1;
                    Q[rear].x = xx;
                    Q[rear].y = yy;
                    if ( !check( xx, yy ) ) return Q[rear].minit;
                    ++rear;
                }
            }
        }

            ++front;
    }

    return -1;
}

int main()
{
    int T;
    scanf( "%d", &T );
    while ( T-- )
    {
        scanf( "%d%d", &r, &c );

        cnt = 0;
        memset( vis, false, sizeof(vis) );
        memset( map, '.', sizeof(map) );

        for ( int i = 1; i <= r; ++i )
        {
            getchar();
            for ( int j = 1; j <= c; ++j )
            {
                map[i][j] = getchar();
                switch( map[i][j] )
                {
                case 'J':
                    start.x = i;
                    start.y = j;
                    start.minit = 0;
                    start.fir = false;
                    vis[i][j] = true;
                    break;

                case 'F':
                    vis[i][j] = true;
                    fire[cnt].x = i;
                    fire[cnt].y = j;
                    fire[cnt].fir = true;
                    fire[ cnt++ ].minit = 0;
                    break;

                case '#':
                    vis[i][j] = true;
                    break;
                }
            }
        }
        int ans = BFS();
        if ( ans == -1 ) puts("IMPOSSIBLE");
        else printf( "%d\n", ans );
    }
    return 0;
}