模板dinic算法

Posted 2020-09-12

dinic算法用于解决最大流问题。

注意每次BFS之前把dist数组清空，源点的dist设为1。

 1 #include<stdio.h>
 2 #include<string.h>
 3 #include<algorithm>
 4 #define inf 1000000000
 5 using namespace std;
 6 int ans,tot,vert,edg,S,T,fr[100005],to[200005],nxt[200005],f[200005];
 7 int que[100005],dist[100005];
 8 bool inq[100005];
 9 void adde(int p,int q,int F)
10 {to[tot]=q;f[tot]=F;nxt[tot]=fr[p];fr[p]=tot++;}
11 bool bfs();
12 int dfs(int,int);
13 int main()
14 {
15     memset(fr,-1,sizeof(fr));
16     scanf("%d%d%d%d",&vert,&edg,&S,&T);
17     int p,q,w,i;
18     for(i=1;i<=edg;i++)
19     {
20         scanf("%d%d%d",&p,&q,&w);
21         adde(p,q,w); adde(q,p,0);
22     }
23     while(bfs()) ans += dfs(S,inf);
24     printf("%d",ans);
25     return 0;
26  } 
27  bool bfs()
28  {
29      memset(dist,0,sizeof(dist));
30      int l=0,r=0,i,t,now;
31      que[++r] = S; dist[S] = 1;
32      while(l<r)
33      {
34          now = que[++l];
35          if(now==T) return true;
36          for(i=fr[now];i!=-1;i=nxt[i])
37          {
38              t = to[i];
39              if(!dist[t]&&f[i])
40              {
41                  dist[t] = dist[now]+1;
42                  que[++r] = t;
43              }
44         }
45     }
46     return false;
47  }
48  int dfs(int now,int maxx)
49  {
50      if(now==T) return maxx;
51      int i,t,ret=0,ss;
52      for(i=fr[now];i!=-1;i=nxt[i])
53      {
54          t = to[i];
55          if(dist[t]==dist[now]+1&&f[i])
56          {
57              ss = dfs(t,min(maxx-ret,f[i]));
58              ret+=ss;
59              f[i] -= ss; f[i^1] += ss;
60              if(ret==maxx) return maxx;
61         }
62     }
63     return ret;
64  }

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