【模板】网络最大流

传送门：

#include <cstdlib>
#include <cstdio>
#include <algorithm>
#include <iostream>
#include <cstring>
#include <queue>
#include <cmath>
using namespace std;
#define ll long long
#define re register
const int N=1e7+10;
const int inf=1e9;
inline void read(int &a)
{
    a=0;
    int d=1;
    char ch;
    while(ch=getchar(),ch>'9'||ch<'0')
        if(ch=='-')
            d=-1;
    a=ch^48;
    while(ch=getchar(),ch>='0'&&ch<='9')
        a=(a<<3)+(a<<1)+(ch^48);
    a*=d;
}
struct note
{
    int v,next,dis;
}edge[N];
int dep[N],head[N],n,m,cnt=-1,maxflow;
inline void add(int u,int v,int dis)
{
    edge[++cnt].next=head[u];
    edge[cnt].v=v;
    edge[cnt].dis=dis;
    head[u]=cnt;
    edge[++cnt].next=head[v];
    edge[cnt].v=u;
    edge[cnt].dis=0;
    head[v]=cnt;
}
queue <int> q;
inline bool bfs(int s,int t)
{
    while(!q.empty())
        q.pop();
    memset(dep,0x7f,sizeof(dep));
    dep[s]=0;
    q.push(s);
    while(!q.empty())
    {
        int now=q.front();
        q.pop();
        for(re int i=head[now];i!=-1;i=edge[i].next)
        {
            if(dep[edge[i].v]>inf&&edge[i].dis)
            {
                dep[edge[i].v]=dep[now]+1;
                q.push(edge[i].v);
            }
        }
    }
    if(dep[t]<inf)
        return 1;
    return 0;
}
inline int dfs(int now,int t,int limit)
{
    if(now==t)
        return limit;
    for(re int i=head[now];i!=-1;i=edge[i].next)
    {
        if(dep[now]+1==dep[edge[i].v]&&edge[i].dis)
        {
            int f=dfs(edge[i].v,t,min(edge[i].dis,limit));
            if(f>0)
            {
                edge[i].dis-=f;
                edge[i^1].dis+=f;
                return f;
            }
        }
    }
    return 0;
}
inline void dinic(int s,int t)
{
    while(bfs(s,t))
    {
        while(int f=dfs(s,t,inf))
            maxflow+=f;
    }
}
int main()
{
    memset(head,0xff,sizeof(head));
    int n,m,s,t;
    read(n),read(m),read(s),read(t);
    for(re int i=1;i<=m;i++)
    {
        int u,v,w;
        read(u),read(v),read(w);
        add(u,v,w);
    }
    dinic(s,t);
    printf("%d",maxflow);
    return 0;
}

比较快的模板

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define re register
const int N=1e5+10;
const int inf=1e9;
inline void read(int &a)
{
    a=0;
    int d=1;
    char ch;
    while(ch=getchar(),ch>'9'||ch<'0')
        if(ch=='-')
            d=-1;
    a=ch^48;
    while(ch=getchar(),ch>='0'&&ch<='9')
        a=(a<<3)+(a<<1)+(ch^48);
    a*=d;
}
int cur[N],head[N],cnt=-1,maxflow,n,m,dep[N];
struct note{int next,v,dis;}edge[2*N];
queue <int> q;
inline void add(int u,int v,int dis)
{
    edge[++cnt].next=head[u];
    edge[cnt].v=v;
    edge[cnt].dis=dis;
    head[u]=cnt;
}
inline bool bfs(int s,int t)
{
    while(!q.empty()) q.pop();
    for(re int i=1;i<=n;i++)
        cur[i]=head[i];
    memset(dep,0x7f,sizeof(dep));
    q.push(s);
    dep[s]=0;
    while(!q.empty())
    {
        int now=q.front();
        q.pop();
        for(re int i=head[now];i!=-1;i=edge[i].next)
        {
            if(dep[edge[i].v]>inf&&edge[i].dis)
            {
                dep[edge[i].v]=dep[now]+1;
                q.push(edge[i].v);
            }
        }
    }
    if(dep[t]<inf)
        return true;
    return false;
}
inline int dfs(int now,int t,int limit)
{
    if(!limit||now==t)
        return limit;
    int flow=0,f;
    for(re int i=cur[now];i!=-1;i=edge[i].next)
    {
        cur[now]=i;
        if(dep[now]+1==dep[edge[i].v]&&(f=dfs(edge[i].v,t,min(limit,edge[i].dis))))
        {
            flow+=f;
            edge[i].dis-=f;
            edge[i^1].dis+=f;
            limit-=f;
            if(!limit)
                break;
        }
    }
    return flow;
}
inline void dinic(int s,int t) {while(bfs(s,t)) maxflow+=dfs(s,t,inf);}
int main()
{
    int s,t;
    memset(head,0xff,sizeof(head));
    read(n),read(m),read(s),read(t);
    for(re int i=1;i<=m;i++)
    {
        int u,v,w;
        read(u);
        read(v);
        read(w);
        add(u,v,w);
        add(v,u,0);
    }
    dinic(s,t);
    printf("%d",maxflow);
    return 0;
}