bzoj3504: [Cqoi2014]危桥 网络流

一种网络流建图的思路吧，改天最好整理一波网络流建图思路

 #include <bits/stdc++.h>
 using namespace std;
 int n,h,t,a1,a2,an,b1,b2,bn,flow,now;char ch;
 int dis[],l[],d[][];char c[][];
 char getch()
 {
     for(ch=getchar();ch!='O' && ch!='N' && ch!='X';ch=getchar());
     return ch;
 }
 bool bfs()
 {
     for(int i=;i<=n+;i++)
         dis[i]=;
     for(h=,t=,l[]=,dis[]=;h<=t;h++)
         for(int i=;i<=n+;i++)
             if(d[l[h]][i] && !dis[i])
                 l[++t]=i,dis[i]=dis[l[h]]+;
     return dis[n+];
 }
 int dfs(int now,int maxflow)
 {
     if(now==n+) return maxflow;
     int flow=;
     for(int i=;i<=n+;i++)
     if(dis[i]==dis[now]+ && d[now][i])
     {
         int thi=dfs(i,min(maxflow,d[now][i]));
         d[now][i]-=thi;d[i][now]+=thi;
         maxflow-=thi;flow+=thi;
         if(maxflow==) return flow;
     }
     if(flow==)
         dis[now]=-;
     return flow;
 }
 void INIT()
 {
     for(int i=;i<=n;i++)
         for(int j=;j<=n;j++)
         switch(c[i][j])
         {
             case'O':d[j][i]=d[i][j]=;break;
             case'N':d[j][i]=d[i][j]=flow;break;
             case'X':d[j][i]=d[i][j]=;break;
         }
     for(int i=;i<=n+;i++)
         d[][i]=d[i][]=d[i][n+]=d[n+][i]=;
     d[a1][]=d[][a1]=an<<;d[b1][]=d[][b1]=bn<<;
     d[a2][n+]=d[n+][a2]=an<<;d[b2][n+]=d[n+][b2]=bn<<;
     now=;
 }
 int main()
 {
     while(~scanf("%d%d%d%d%d%d%d",&n,&a1,&a2,&an,&b1,&b2,&bn))
     {
     a1++;a2++;b1++;b2++;
     flow=an+bn<<;
     for(int i=;i<=n;i++)
         for(int j=;j<=n;j++)
             c[i][j]=getch();
     INIT();
     while(now<flow && bfs()) now=now+dfs(,flow);
     if(now<flow)
     {
         puts("No");
         continue;
     }
     swap(b1,b2);
     INIT();
     while(now<flow && bfs()) now=now+dfs(,flow);
     if(now<flow)
         puts("No");
     else
         puts("Yes");
     }
     return ;
 }