【BFS】uva11624Fire!

/*
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;
    }

-----------

【BFS】uva11624Fire!,布布扣,bubuko.com