最大流dicnic——hdu1532模板题

Posted 2021-12-28 zsben991126

#include<bits/stdc++.h>
using namespace std;
#define maxn 1005
#define ll long long

const ll inf = 0x3f3f3f3f3f3f3f3f;
 
struct Edgell to,nxt,w;e[maxn<<1];
int head[maxn],tot,n,m;
void init()
    memset(e,0,sizeof e);
    memset(head,-1,sizeof head);
    tot=0;

void add(ll u,ll v,ll w)
    e[tot].to=v;e[tot].nxt=head[u];e[tot].w=w;head[u]=tot++; 


int d[maxn];
bool bfs()//在残量网络上构造分层图 
    memset(d,0,sizeof d);
    
    queue<int>q;
    while(q.size())q.pop();
    q.push(1);d[1]=1;
    
    while(q.size())
        int x=q.front();q.pop();
        for(int i=head[x];i!=-1;i=e[i].nxt)
            int y=e[i].to;
            if(d[y] || e[i].w==0)continue;
            q.push(y);
            d[y]=d[x]+1;
            if(y==n)return 1;
        
    
    return 0;

int dinic(int x,ll flow)
    if (x==n)return flow;
    ll rest=flow;
    for(int i=head[x];i!=-1 && rest>0;i=e[i].nxt)
        int y=e[i].to;
        if(e[i].w==0 || d[y]!=d[x]+1)continue;
        ll k=dinic(y,min(rest,e[i].w));
        if(!k)    d[y]=0;    //y点已经被增广完毕
        e[i].w-=k; e[i^1].w+=k;
        rest-=k;
    
    return flow-rest;
 


int main()
    while(cin>>m>>n)
        init();
        for(int i=1;i<=m;i++)
            ll u,v,w;
            cin>>u>>v>>w;
            add(u,v,w);
            add(v,u,0);
        
        ll flow=0,ans=0;
        while(bfs())
            while(flow=dinic(1,inf))
                ans+=flow;
        cout<<ans<<‘\n‘;