bzoj3504: [Cqoi2014]危桥 网络流

Posted 2020-08-28 汪立超

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

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 int n,h,t,a1,a2,an,b1,b2,bn,flow,now;char ch;
 4 int dis[52],l[52],d[52][52];char c[52][52];
 5 char getch()
 6 {
 7     for(ch=getchar();ch!=‘O‘ && ch!=‘N‘ && ch!=‘X‘;ch=getchar());
 8     return ch;
 9 }
10 bool bfs()
11 {
12     for(int i=1;i<=n+1;i++)
13         dis[i]=0;
14     for(h=1,t=1,l[1]=0,dis[0]=1;h<=t;h++)
15         for(int i=1;i<=n+1;i++)
16             if(d[l[h]][i] && !dis[i])
17                 l[++t]=i,dis[i]=dis[l[h]]+1;
18     return dis[n+1];
19 }
20 int dfs(int now,int maxflow)
21 {
22     if(now==n+1) return maxflow;
23     int flow=0;
24     for(int i=0;i<=n+1;i++)
25     if(dis[i]==dis[now]+1 && d[now][i])
26     {
27         int thi=dfs(i,min(maxflow,d[now][i]));
28         d[now][i]-=thi;d[i][now]+=thi;
29         maxflow-=thi;flow+=thi;
30         if(maxflow==0) return flow;
31     }
32     if(flow==0)
33         dis[now]=-1;
34     return flow;
35 }
36 void INIT()
37 {
38     for(int i=1;i<=n;i++)
39         for(int j=1;j<=n;j++)
40         switch(c[i][j])
41         {
42             case‘O‘:d[j][i]=d[i][j]=2;break;
43             case‘N‘:d[j][i]=d[i][j]=flow;break;
44             case‘X‘:d[j][i]=d[i][j]=0;break;
45         }
46     for(int i=0;i<=n+1;i++)
47         d[0][i]=d[i][0]=d[i][n+1]=d[n+1][i]=0;
48     d[a1][0]=d[0][a1]=an<<1;d[b1][0]=d[0][b1]=bn<<1;
49     d[a2][n+1]=d[n+1][a2]=an<<1;d[b2][n+1]=d[n+1][b2]=bn<<1;
50     now=0;
51 }
52 int main()
53 {
54     while(~scanf("%d%d%d%d%d%d%d",&n,&a1,&a2,&an,&b1,&b2,&bn))
55     {
56     a1++;a2++;b1++;b2++;
57     flow=an+bn<<1;
58     for(int i=1;i<=n;i++)
59         for(int j=1;j<=n;j++)
60             c[i][j]=getch();
61     INIT();
62     while(now<flow && bfs()) now=now+dfs(0,flow);
63     if(now<flow)
64     {
65         puts("No");
66         continue;
67     }
68     swap(b1,b2);
69     INIT();
70     while(now<flow && bfs()) now=now+dfs(0,flow);
71     if(now<flow)
72         puts("No");
73     else
74         puts("Yes");
75     }
76     return 0;
77 }