HDU:4771 Stealing Harry Potter's Precious

杭州现场赛的题目，虽然大神们都说水，但我感觉还是不错的，还适合我这个水平做。

用bfs求出各个宝物之间的最短距离以及和Dudely之间的距离，然后用dfs枚举Dudely访问各个宝物的顺序，最后比较出距离和的最小值即可。

 

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<queue>
#define INF 2139062143
#define MAXN 105
using namespace std;
char grid[MAXN][MAXN];
int flag[MAXN][MAXN],N,M,n,ans,x[5],y[5],dis[5][5];
bool used[10],vis[MAXN][MAXN];
int MM[4][2]= {{1,0},{-1,0},{0,1},{0,-1}};
struct Point
{
    int x,y,step;
    Point(int a,int b,int c):x(a),y(b),step(c) {}
};
void bfs(int xx,int yy)
{

    int cur=flag[xx][yy];
    queue<Point> q;
    memset(vis,0,sizeof(vis));
    q.push(Point(xx,yy,0));
    vis[xx][yy]=true;
    while(!q.empty())
    {
        Point u=q.front();
        q.pop();
        for(int i=0; i<4; ++i)
        {
            int ta=u.x+ MM[i][0],tb=u.y+MM[i][1];
            if(ta<1||tb<1||ta>N||tb>M) continue;
            if(vis[ta][tb]||grid[ta][tb]=='#') continue;
            vis[ta][tb]=true;
            if(flag[ta][tb]!=-1)
                dis[cur][flag[ta][tb]]=u.step+1;
            q.push(Point(ta,tb,u.step+1));
        }
    }
}
void dfs(int now,int res,int cur)
{
    if(cur==n)
        ans=min(ans,res);
    else
    {
        for(int i=1; i<=n; ++i)
            if(!used[i]&&dis[now][i]<INF)
            {
                used[i]=true;
                dfs(i,res+dis[now][i],cur+1);
                used[i]=false;
            }
    }
}
int main()
{
    while(scanf("%d%d",&N,&M)&&!(!N&&!M))
    {
        memset(flag,-1,sizeof(flag));
        memset(grid,0,sizeof(grid));
        memset(used,0,sizeof(used));
        memset(dis,0x7f,sizeof(dis));
        for(int i=1; i<=N; ++i)
            scanf("%s",grid[i]+1);
        for(int i=1; i<=N; ++i)
            for(int j=1; j<=M; ++j)
                if(grid[i][j]=='@')
                {
                    x[0]=i;
                    y[0]=j;
                    flag[i][j]=0;
                    break;
                }
        scanf("%d",&n);
        for(int i=1; i<=n; ++i)
        {
            scanf("%d%d",&x[i],&y[i]);
            flag[x[i]][y[i]]=i;
        }

        for(int i=0; i<=n; ++i)
            bfs(x[i],y[i]);
        ans=INF;
        dfs(0,0,0);
        if(ans==INF) printf("-1\n");
        else
            printf("%d\n",ans);
    }
    return 0;
}