【BFS】uva11624Fire!

来源：互联网发布：网络语打卡的意思编辑：程序博客网时间：2024/06/05 15:51
/*bfs宽度遍历--------------------------------------------------------------------------对人和火同时进行bfs,,注意应该先火后人，即如果在人到达该格子前，格子已经着火则不应该走，最后人走到边界无路可走，则IMPOSSIBLE！！！！！！！！！！！！---------------------------------------------------------------------------两次bfs:bfs1();火bfs()人：先bfs1后bfs();;;;;;;;;;;;;;;;;;;;;;;;;;;;或者计算格子着火的时间--------------------------------------------------------------------------for(int i=0; i<r; i++)因为火格不止一个，应该for循环{    for(int j=0; j<c; j++)    {        if(g[i][j] == 'F')火进入队列        {            q[rear].x = j;            q[rear].y = i;            q[rear].step = 0;step置零            q[rear++].flag = 1;标记为火格子        }    }}-----------------------------------------------------------------------------q[rear].x = fx;人（的起点）进入队列q[rear].y = fy;q[rear].step = 0;q[rear++].flag = 0;-------------------------------------------------------------------------------if(q[front].flag)火点进行扩展{    for(int i=0; i<4; i++)每次扩展都有4个方向    {        xx = q[front].x + step_x[i];更新扩展点的位置        yy = q[front].y + step_y[i];        if(xx < 0 || xx >= c || yy < 0 || yy >= r || g[yy][xx] == '#' || g[yy][xx] == 'F')如果越界，遇到火，障碍物continue            continue;        g[yy][xx] = 'F';火蔓延至此        q[rear].x = xx;扩展点变为当前点        q[rear].y = yy;        q[rear].flag = 1;标记为火        q[rear++].step = q[front].step+1;每次时间加1    }}---------------------------------------------------------------------------------------for(int i=0; i<4; i++)人扩展{    xx = q[front].x + step_x[i];    yy = q[front].y + step_y[i];    if(vis[yy][xx] || g[yy][xx] == 'F' || g[yy][xx] == '#')        continue;    if(xx < 0 || xx >= c || yy < 0 || yy >= r)        return q[front].step+1;    vis[yy][xx] = 1;    q[rear].x = xx;    q[rear].y = yy;    q[rear].flag = 0;    q[rear].step = q[front].step + 1;    ++rear;------------------------------------------------------------------------------------*/#include <iostream>#include <cstdio>#include <cstring>#define INF 0x3f3f3f3f    using namespace std;    const int MAXN = 1010;    struct node    {        int x, y;        int step;        int flag;    } q[MAXN*MAXN];    int r, c;    int fx, fy;    int step_x[4] = {1, -1, 0, 0};    int step_y[4] = {0, 0, 1, -1};    char g[MAXN][MAXN];    int vis[MAXN][MAXN];    int bfs()    {        int front = 0, rear = 0;        memset(vis, 0, sizeof(vis));        for(int i=0; i<r; i++)        {            for(int j=0; j<c; j++)            {                if(g[i][j] == 'F')                {                    q[rear].x = j;                    q[rear].y = i;                    q[rear].step = 0;                    q[rear++].flag = 1;                }            }        }        q[rear].x = fx;        q[rear].y = fy;        q[rear].step = 0;        q[rear++].flag = 0;        while(front < rear)        {            int xx = q[front].x;            int yy = q[front].y;            if(q[front].flag)            {                for(int i=0; i<4; i++)                {                    xx = q[front].x + step_x[i];                    yy = q[front].y + step_y[i];                    if(xx < 0 || xx >= c || yy < 0 || yy >= r || g[yy][xx] == '#' || g[yy][xx] == 'F')                        continue;                    g[yy][xx] = 'F';                    q[rear].x = xx;                    q[rear].y = yy;                    q[rear].flag = 1;                    q[rear].step = q[front].step+1;                    ++rear;                }            }            else            {                for(int i=0; i<4; i++)                {                    xx = q[front].x + step_x[i];                    yy = q[front].y + step_y[i];                    if(vis[yy][xx] || g[yy][xx] == 'F' || g[yy][xx] == '#')                        continue;                    if(xx < 0 || xx >= c || yy < 0 || yy >= r)                        return q[front].step+1;                    vis[yy][xx] = 1;                    q[rear].x = xx;                    q[rear].y = yy;                    q[rear].flag = 0;                    q[rear++].step = q[front].step + 1;                }            }            front++;        }        return 0;    }    int main()    {        //freopen("input.txt","r",stdin);        int T;        cin>>T;        while(T--)        {            scanf("%d%d",&r,&c);            fx = fy = -1;            getchar();            for(int i=0; i<r; i++)            {                gets(g[i]);                if(fx == -1)                {                    for(int j=0; j<c; j++)                    {                        if(g[i][j] == 'J')                        {                            fx = j;                            fy = i;                            break;                        }                    }                }            }            int time = bfs();            if(time)                printf("%d\n",time);            else                printf("IMPOSSIBLE\n");        }        return 0;    }
-----------
0 0