网络流最大流模板

Posted 2021-01-10 profish

题目链接：

http://poj.org/problem?id=1273

#include<iostream>
#include<cstdio>
#include<iomanip>
#include<cmath>
#include<algorithm>
#include<vector>
#include<cstring>
#include<queue>
#include<map>
#include<string>
#include<stack>
#define fi first
#define se second
#define INF 0x3f3f3f3f
#define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define pqueue priority_queue
#define NEW(a,b) memset(a,b,sizeof(a))
const double pi=4.0*atan(1.0);
const double e=exp(1.0);
const int maxn=1e4+8;
typedef long long LL;
typedef unsigned long long ULL;
const LL mod=1e9+7;
const ULL base=1e7+7;
using namespace std;
struct node{
    int to,nxt,v;
}g[maxn];
int head[maxn],curedge[maxn],dis[maxn],cnt=0,n;
void add(int x,int y,int v){
    g[cnt].nxt=head[x];
    g[cnt].to=y;
    g[cnt].v=v;
    head[x]=cnt++;
}
bool bfs(int s,int t){
    memset(dis,INF,sizeof(dis));
    dis[s]=0;
    queue<int> que;
    while(!que.empty()) {que.pop();}
    que.push(s);
    while(!que.empty()){
        int k=que.front();
        //cout<<k<<endl;
        que.pop();
        int tt=head[k];
        while(tt!=-1){
            if(dis[g[tt].to]==INF&&g[tt].v>0){
                dis[g[tt].to]=dis[k]+1;
                que.push(g[tt].to);
            }
            tt=g[tt].nxt;
        }
    }
    return dis[t]!=INF;
}
int dfs(int u,int t,int flow){
    if(u==t) return flow;
    //cout<<u<<endl;
    int &i=curedge[u];
    int delta=flow;
    while(i!=-1){
        if(dis[g[i].to]==dis[u]+1){
            int d=dfs(g[i].to,t,min(delta,g[i].v));
            g[i].v-=d;
            g[i^1].v+=d;
            delta-=d;
            if(delta==0) break;
        }
        i=g[i].nxt;
    }
    return flow-delta;
}
int dinic(int s,int t){
    int ans=0;
    while(bfs(s,t)){
        for(int i=1;i<=t;i++){
            curedge[i]=head[i];
        }
        ans+=dfs(s,t,INF);
    }
    return ans;
}
int main(){
    int s,t;
    s=1;
    while(~scanf("%d%d",&n,&t)){
        int x,y,v;
        memset(head,-1,sizeof(head));
        for(int i=1;i<=n;i++){
            scanf("%d%d%d",&x,&y,&v);
            add(x,y,v);add(y,x,0);
        }
    //cout<<‘a‘<<endl;
        printf("%d
",dinic(s,t));
    }
}