dinic模版

Posted 2020-10-10 ChenThree

#include<cstdio> 
#include<cstring>
#include<cmath>
#include<iostream>
#include<algorithm>
#include<queue>
#include<set>
#define maxint (2147483647)
#define l(a) ((a)<<1)
#define r(a) ((a)<<1|1)
#define b(a) (2<<(a))
#define rep(i,a,b) for(int i=a;i<=(b);i++)
#define repe(i,e) for(edge*e=fir[i];e;e=e->next)
#define clr(a) memset(a,0,sizeof(a))
typedef long long ll;
using namespace std;
int readint(){
    int t=0,f=1;char c=getchar();
    while(!isdigit(c)){
        if(c==‘-‘) f=-1;
        c=getchar();
    }
    while(isdigit(c)){
        t=(t<<3)+(t<<1)+c-‘0‘;
        c=getchar();
    }
    return t*f;
}
const int maxn=10009,maxm=200009;
int n,m,S,T,d[maxn];
struct edge{
    int v,w;
    edge*next,*r;
}e[maxm],*fir[maxn],*cur[maxn],*pt=e;
void add(int u,int v,int w){
    pt->v=v;pt->w=w;pt->next=fir[u];
    fir[u]=pt++;
}
void addedge(int u,int v,int w){
    add(u,v,w);add(v,u,0);
    fir[u]->r=fir[v];fir[v]->r=fir[u];
}
bool bfs(){
    queue<int>Q;Q.push(S);
    clr(d);d[S]=1;
    while(!Q.empty()){
        int x=Q.front();Q.pop();
        repe(x,e){
            if(e->w&&!d[e->v]){
                d[e->v]=d[x]+1;Q.push(e->v);
            }
        }
    }
    if(d[T]) rep(i,1,n) cur[i]=fir[i];
    return d[T];
}
int dfs(int x,int w){
    if(x==T||!w) return w;
    int f=0;
    for(edge*&e=cur[x];e;e=e->next){
        if(e->w&&d[e->v]==d[x]+1){
            int g=dfs(e->v,min(e->w,w));
            if(g>0){
                f+=g;
                e->w-=g;e->r->w+=g;
                if(!(w-=g)) break;
            }
        }
    }
    return f;
}
int main(){
    //freopen("#input.txt","r",stdin);
    //freopen("#output.txt","w",stdout);
    n=readint();m=readint();S=readint();T=readint();
    rep(i,1,m){
        int u=readint(),v=readint(),w=readint();
        addedge(u,v,w);
    }
    int ans=0;
    while(bfs()) ans+=dfs(S,maxint);
    printf("%d\n",ans);
    //fclose(stdin);
    //fclose(stdout);
    return 0;
}