loj 101 最大流

Posted 2020-10-22 jack_yyc

冬令营送到我脸上的20分都没拿全

心态爆炸

冬令营前一天学的dinic

后一天才发出来

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cmath>
 4 #include<cstdlib>
 5 #include<cstring>
 6 #include<algorithm>
 7 #include<vector>
 8 #include<queue>
 9 #define inf 2139062143
10 #define ll long long
11 #define MAXN 1000100
12 using namespace std;
13 inline int read()
14 {
15     int x=0,f=1;char ch=getchar();
16     while(!isdigit(ch)) {if(ch==‘-‘) f=-1;ch=getchar();}
17     while(isdigit(ch)) {x=x*10+ch-‘0‘;ch=getchar();}
18     return x*f;
19 }
20 struct Dinic
21 {
22     int fst[MAXN],nxt[MAXN<<3],to[MAXN<<3],val[MAXN<<3],cnt,n,m,s,t;
23     Dinic() {cnt=0;memset(fst,0xff,sizeof(fst));}
24     void add(int u,int v,int w) {nxt[cnt]=fst[u],fst[u]=cnt,to[cnt]=v,val[cnt++]=w;}
25     int q[MAXN],dep[MAXN],cur[MAXN],vis[MAXN],tot;
26     int BFS()
27     {
28         int l=1,r=0;
29         memset(dep,0xff,sizeof(dep));
30         vis[t]=++tot,q[++r]=t;
31         while(l<=r)
32         {
33             int x=q[l++];cur[x]=fst[x];
34             for(int i=fst[x];i!=-1;i=nxt[i])
35             {
36                 if(val[i^1]&&vis[to[i]]!=tot) 
37                 {
38                     vis[to[i]]=tot,dep[to[i]]=dep[x]+1,q[++r]=to[i];
39                     if(to[i]==s) return 1;
40                 }
41             }
42         }
43         return vis[s]==tot;
44     }
45     int DFS(int x,int a)
46     {
47         if(x==t||!a) return a;
48         int flow=0,f;
49         for(int& i=cur[x];i!=-1;i=nxt[i])
50         {
51             if(val[i]&&dep[to[i]]==dep[x]-1&&(f=DFS(to[i],min(a,val[i]))))
52             {
53                 val[i]-=f,val[i^1]+=f,flow+=f,a-=f;
54                 if(!a) break;
55             }
56         }
57         return flow;
58     }
59     ll solve()
60     {
61         ll ans=0;int f;
62         while(BFS())
63         {
64             memcpy(cur,fst,sizeof(cur));
65             while(f=DFS(s,inf)) ans+=f;
66         }
67         return ans;
68     }
69 }D;
70 int main()
71 {
72     int k;
73     D.n=read(),k=D.m=read(),D.s=read(),D.t=read();
74     int u,v,w;
75     for(int i=1;i<=k;i++) {u=read(),v=read(),w=read();D.add(u,v,w);D.add(v,u,0);}
76     printf("%lld",D.solve());
77 }

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