【Luogu】P3376网络最大流模板（Dinic）

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cctype>

inline long long read(){
    long long num=0,f=1;
    char ch=getchar();
    while(!isdigit(ch)){
        if(ch=='-')    f=-1;
        ch=getchar();
    }
    while(isdigit(ch)){
        num=num*10+ch-'0';
        ch=getchar();
    }
    return num*f;
}

struct Edge{
    int next,to,val;
}edge[1000010];
int head[10010],num=-1;
inline void add(int from,int to,int val){
    edge[++num]=(Edge){    head[from],to,val};
    head[from]=num;
}

bool vis[10010];
int dfn[10010];
int f[100010],h,t=1;
int n,m,Start,End;

bool bfs(){
    memset(vis,0,sizeof(vis));
    f[1]=Start;vis[Start]=1;dfn[Start]=1;h=0;t=1;
    while(h++<t){
        int from=f[h];
        for(int i=head[from];i!=-1;i=edge[i].next){
            int to=edge[i].to;
            if(vis[to]||(!edge[i].val))    continue;
            dfn[to]=dfn[from]+1;
            vis[to]=1;
            f[++t]=to;
        }
    }
    return vis[End];
}

int dfs(int x,int val){
    if(x==End)    return val;
    vis[x]=1;
    for(int i=head[x];i!=-1;i=edge[i].next){
        int to=edge[i].to;
        if(dfn[to]==dfn[x]+1&&!vis[to]&&edge[i].val>0){
            int now=dfs(to,std::min(edge[i].val,val));
            if(now>0){
                edge[i].val-=now;
                edge[i^1].val+=now;
                return now;
            }
        }
    }
}

int ans;

int main(){
    memset(head,-1,sizeof(head));
    n=read(),m=read(),Start=read(),End=read();
    for(int i=1;i<=m;++i){
        int from=read(),to=read(),val=read();
        add(from,to,val);
        add(to,from,0);
    }
    while(bfs()){
        memset(vis,0,sizeof(vis));
        int now=dfs(Start,0x7fffffff);
        if(!now)    break;
        ans+=now;
    }
    printf("%d",ans);
    return 0;
}