FZU-2150.FireGame.(BFS))

　　本题大意：给出一个n * m的地，‘#’ 代表草， ‘.’代表陆地，每次选择这片地里的两片草，可选相等的草，选择的两片草初始状态为被燃状态，每一分钟被点燃的草会将身边的四连块点。问你需要对于给定的这片地最少需要多少分钟能燃烧完，燃烧不完输出 -1.

　　本题思路：很直观的一道题，枚举所有可能开始燃烧的点，更新最小值就行，无法燃烧完则是输出-1。

　　参考代码：

//要勤于思考，思考使人明智，不要总是因为一两个点没有想到就浪费时间
#include <cstdio>
#include <queue>
#include <cmath>
#include <cstring>
#include <vector>
using namespace std;

struct node {
    int x, y, step;
}now, Next;

const int maxn = 10 + 2, INF = 0x3f3f3f3f;
int n, m, t, ans, connected_block, maxstep, Case = 0;
char maze[maxn][maxn];
bool vis_index[maxn][maxn];
vector <node> grass;

bool check () {
    for(int i = 0; i < n; i ++)
        for(int j = 0; j < m; j ++)
            if(maze[i][j] == '#' && !vis_index[i][j]) return false;
    return true;
}

bool useful(int x, int y) {
    return (x >= 0 && y >= 0 && x < n && y < m && maze[x][y] == '#' && !vis_index[x][y]);
}

void Init() {
    grass.clear();
    memset(vis_index, false, sizeof vis_index);
    ans = INF, connected_block = 0;
}

int bfs(node n1, node n2) {
    queue < node> Q;
    memset(vis_index, false, sizeof vis_index);
    Q.push(n1), Q.push(n2);
    maxstep = 0;
    while(!Q.empty()) {
        now = Q.front();
        Q.pop();
        if(vis_index[now.x][now.y]) continue;
        maxstep = now.step;
        vis_index[now.x][now.y] = true;
        for(int dx = -1; dx <= 1; dx ++) {
            for(int dy = -1; dy <= 1; dy ++) {
                if(abs(dx - dy) == 1) {
                    if(useful(now.x + dx, now.y + dy)) {
                        Next.x = now.x + dx, Next.y = now.y + dy, Next.step = now.step + 1;
                        Q.push(Next);
                    }
                }   
            }
        }
    }
    return maxstep;
}

int main () {
    scanf("%d", &t);
    while(t --) {
        Init();
        scanf("%d %d", &n, &m);
        getchar();
        for(int i = 0; i < n; i ++) {
            for(int j = 0; j < m; j ++) {
                maze[i][j] =getchar();
                if(maze[i][j] == '#') {
                    node g;
                    g.x = i, g.y = j, g.step = 0;
                    grass.push_back(g);
                }
            }
            getchar();
        }
        //Find answer
        for(int i = 0; i < grass.size(); i ++)
            for(int j = i; j < grass.size(); j ++) {
                grass[i].step = 0, grass[j].step = 0;
                int temp = min(bfs(grass[i], grass[j]), ans);
                if(check()) ans = min(temp, ans);
            }
        printf("Case %d: ", ++ Case);
        if(ans == INF) printf("-1
");
        else printf("%d
", ans);
    }
    return 0;
}