(FZU 2150) Fire Game (bfs)

Posted 2020-08-27

题目链接：http://acm.fzu.edu.cn/problem.php?pid=2150

Problem Description

Fat brother and Maze are playing a kind of special (hentai) game on an N*M board (N rows, M columns). At the beginning, each grid of this board is consisting of grass or just empty and then they start to fire all the grass. Firstly they choose two grids which are consisting of grass and set fire. As we all know, the fire can spread among the grass. If the grid (x, y) is firing at time t, the grid which is adjacent to this grid will fire at time t+1 which refers to the grid (x+1, y), (x-1, y), (x, y+1), (x, y-1). This process ends when no new grid get fire. If then all the grid which are consisting of grass is get fired, Fat brother and Maze will stand in the middle of the grid and playing a MORE special (hentai) game. (Maybe it’s the OOXX game which decrypted in the last problem, who knows.)

You can assume that the grass in the board would never burn out and the empty grid would never get fire.

Note that the two grids they choose can be the same.

Input

The first line of the date is an integer T, which is the number of the text cases.

Then T cases follow, each case contains two integers N and M indicate the size of the board. Then goes N line, each line with M character shows the board. “#” Indicates the grass. You can assume that there is at least one grid which is consisting of grass in the board.

1 <= T <=100, 1 <= n <=10, 1 <= m <=10

Output

For each case, output the case number first, if they can play the MORE special (hentai) game (fire all the grass), output the minimal time they need to wait after they set fire, otherwise just output -1. See the sample input and output for more details.

Sample Input

4 3 3 .#. ### .#. 3 3 .#. #.# .#. 3 3 ... #.# ... 3 3 ### ..# #.#

Sample Output

Case 1: 1

Case 2: -1

Case 3: 0

Case 4: 2

题目大意：两个人玩关于火的游戏，在一个地图上#表示干草，开始可以点燃两个干草（可重叠），火每秒可向周围四个方向蔓延，空白处不能过，问所有的干草是否能燃尽，如能，输出最快时间

思路：题中数据不大，把所有干草坐标统计一下，每次选出两个遍历一遍，统计所有可能的最小值

#include<stdio.h>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<math.h>
#include<queue>
using namespace std;
#define INF 0x3f3f3f3f
#define ll long long
#define met(a,b) memset(a,b,sizeof(a))
#define N 109
int vis[N][N];
char str[N][N];
int dir[4][2]={{1,0},{-1,0},{0,1},{0,-1}};
int k,n,m;
struct node
{
    int x,y,temp;
}a[N];///统计干草的坐标
int pan()///判断干草是否都能被点燃
{
    int x,y;
    for(int i=0;i<k;i++)
    {
        x=a[i].x;y=a[i].y;
        if(!vis[x][y])
            return 0;
    }
    return 1;
}
int bfs(node a,node b)
{
    int team=0;
    met(vis,0);
    queue<node>Q;
    node q,p;
    Q.push(a);Q.push(b);
    vis[a.x][a.y]=1;vis[b.x][b.y]=1;
    while(Q.size())
    {
        q=Q.front();
        Q.pop();
        for(int i=0;i<4;i++)
        {
            p.x=q.x+dir[i][0];
            p.y=q.y+dir[i][1];
            p.temp=q.temp+1;
            if(p.x>=0 && p.x<n&& p.y>=0 && p.y<m && str[p.x][p.y]==‘#‘ && !vis[p.x][p.y])
            {
                vis[p.x][p.y]=1;
                team=max(team,p.temp);
                Q.push(p);
            }
        }
    }
    if(pan())
        return team;
    else
        return INF;
}
int main()
{
    int t,con=1;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d %d",&n,&m);
        for(int i=0;i<n;i++)
            scanf("%s",str[i]);
        k=0;
        for(int i=0;i<n;i++)
        {
            for(int j=0;j<m;j++)
            {
                if(str[i][j]==‘#‘)
                {
                    a[k].x=i;
                    a[k].y=j;
                    a[k++].temp=0;
                }
            }
        }
        int ans=INF;
        for(int i=0;i<k;i++)
        {
            for(int j=i;j<k;j++)
            {
                ans=min(bfs(a[i],a[j]),ans);
            }
        }
        printf("Case %d: ",con++);
        if(ans==INF)
            printf("-1\n");
        else
            printf("%d\n",ans);
    }
    return 0;
}