luogu P3376 模板网络最大流 模板

Posted 2020-12-12 qingyuyyyyy

#include <iostream>
#include <cstdio>
#include <cstring>
#define N 200005
using namespace std;
#define int long long
int n,m,S,T,tmp1,tmp2,tot;
int idx,head[N],cur[N],q[N],ans1[N],ans2[N];
int e[N],ne[N],w[N];
bool b[N];
int r[N],c[N];
inline void add(int u,int v,int f)
{
    e[idx]=v;
    w[idx]=f;
    ne[idx]=head[u];
    head[u]=idx++;
}
inline bool bfs()
{
    int f=0,t=0;
    memset(cur,-1,sizeof(cur));
    q[t++]=S;
    cur[S]=0;
    while(f<t)
    {
        int now=q[f++];
        for(int i=head[now]; ~i; i=ne[i])
        {
            int v=e[i];
            if(cur[v]==-1&&w[i])
            {
                cur[v]=cur[now]+1;
                q[t++]=v;
            }
        }
    }
    if(cur[T]!=-1)
        return 1;
    return 0;
}
inline int dfs(int x,int f)
{
    if(x==T)
        return f;
    int w1,used=0;
    for(int i=head[x]; ~i; i=ne[i])
    {
        int v=e[i];
        if(cur[v]==cur[x]+1&&w[i])
        {
            w1=dfs(v,min(f-used,w[i]));
            w[i]-=w1;
            w[i^1]+=w1;
            used+=w1;
            if(used==f)
                return f;
        }
    }
    if(!used)
        cur[x]=-1;
    return used;
}
void dinic()
{
    while(bfs())
        tot+=dfs(S,0x3f3f3f3f);
}
signed main()
{
    memset(head,-1,sizeof head);
    cin>>n>>m>>S>>T;
    for(int i=1; i<=m; i++)
    {
        int a,b,c;
        cin>>a>>b>>c;
        add(a,b,c);
        add(b,a,0);
    }
    dinic();
    cout<<tot<<endl;
    return 0;
}