求助Dinic 37pts

记录详情: https://www.luogu.com.cn/record/63156415

代码:

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int M=5010;

struct node{
    int to,next,dis;
}edge[M<<1];
int head[M],cnte;
void add(int u,int v,int w){
    edge[++cnte].to=v;
    edge[cnte].dis=w;
    edge[cnte].next=head[u];
    head[u]=cnte;
}

int n,m,s,t,ans;

int dis[M];
bool bfs(){
    for(int i=0;i<M;i++) dis[i]=0;
    dis[s]=1;
    queue<int>q;
    q.push(s);
    while(!q.empty()){
        int u=q.front();q.pop();
        for(int i=head[u];~i;i=edge[i].next){
            int v=edge[i].to;
            if(!dis[v]&&edge[i].dis>0) dis[v]=dis[u]+1,q.push(v);
        }
    }
    return dis[t];
}

int dfs(int u,int in){
    if(u==t) return in;
    int out=0;
    for(int i=head[u];~i&&in>0;i=edge[i].next){
        int v=edge[i].to;
        if(edge[i].dis>0&&dis[v]==dis[u]+1){
            int res=dfs(v,min(edge[i].dis,in));
            edge[i].dis-=res;
            edge[i^1].dis+=res;
            in-=res,out+=res;
        }
    }
    if(out==0) dis[u]=-100000;
    return out;
}

signed main(){
    for(int i=0;i<M;i++) head[i]=-1;
    scanf("%lld%lld%lld%lld",&n,&m,&s,&t);
    for(int i=1,u,v,w;i<=m;i++){
        scanf("%lld%lld%lld",&u,&v,&w);
        add(u,v,w),add(v,u,0);
    }
    while(bfs()) ans+=dfs(s,1e18);
    printf("%lld",ans);
    return 0;
}