bzoj1295

题解：

如果距离中没有Ｔ个箱子

那么就是可以的

代码：

#include<bits/stdc++.h>  
using namespace std;  
const int N=10005;
const int qx[4]={0,0,1,-1};  
const int qy[4]={1,-1,0,0};   
int a[N],n,m,t,tot,id[350][305],b[N],Map[N][4],dis[1200][1200];  
double ans=0;    
int pan(int x,int y)  
{  
    if (x<1||x>n||y<1||y>m) return false;  
    return true;  
}  
int main()  
{   
    scanf("%d%d%d",&n,&m,&t);  
    char c;  
    tot=0;  
    for (int i=1;i<=n;i++)  
     for (int j=1;j<=m;j++)  
      {  
        c='';  
        while (c!='0'&&c!='1') scanf("%c",&c);  
        id[i][j]=++tot;  
        if (c=='1') a[tot]=1;  
      }  
    memset(Map,0,sizeof(Map));   
    for (int i=1;i<=n;i++)  
     for (int j=1;j<=m;j++)  
      for (int l=0;l<4;l++)  
       if (pan(i+qx[l],j+qy[l])) Map[id[i][j]][l]=id[i+qx[l]][j+qy[l]]; 
    memset(dis,0x3f3f3f3f,sizeof(dis));  
    for (int i=1;i<=tot;i++) dis[i][i]=a[i];  
    queue<int> q;  
    for (int i=1;i<=n;i++)  
     for (int j=1;j<=m;j++)  
      {  
        while (!q.empty()) q.pop();  
        int from=id[i][j];  
        memset(b,false,sizeof(b));  
        b[from]=true;  
        q.push(from);  
        while (!q.empty())  
         {  
            int u=q.front();  
            q.pop();  
            for (int i=0;i<4;i++)
             if (Map[u][i])  
              {  
                int v=Map[u][i];  
                if (dis[from][u]+a[v]<dis[from][v])   
                 {  
                    dis[from][v]=dis[from][u]+a[v];  
                    if (!b[v])  
                     {  
                        b[v]=true;  
                        q.push(v);  
                     }  
                 }  
              }  
            b[u]=false;  
         }  
      }  
    for (int i=1;i<tot;i++)  
     for (int j=i+1;j<=tot;j++)  
      if (dis[i][j]<=t)  
       {  
        int x=i/m+1,y=i%m;  
        if (i%m==0) x--,y=m;  
        int xx=j/m+1,yy=j%m;  
        if (j%m==0) xx--,yy=m;  
        ans=max(ans,sqrt((x-xx)*(x-xx)*1.0+(y-yy)*(y-yy)*1.0));  
       }     
    printf("%.6f",ans);  
    return 0;     
}