网络流Dinic模板

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#define mem(a,b) memset(a,b,sizeof(a))
using namespace std;
const int maxn = 100100, INF = 0x7fffffff;
int d[maxn], head[maxn];
int n, m, s, t;
struct edge{
    int u, v, f, c, next;
}Node[2*maxn];

void add(int u, int v, int c, int f, int i)
{
    Node[i].u = u;
    Node[i].v = v;
    Node[i].f = f;
    Node[i].c = c;
    Node[i].next = head[u];
    head[u] = i;
}


int bfs()
{
    queue<int> Q;
    mem(d,0);
    Q.push(s);
    d[s] = 1;
    while(!Q.empty()){
        int u = Q.front(); Q.pop();
        for(int i=head[u]; i!=-1; i=Node[i].next)
        {
            edge e = Node[i];
            if(!d[e.v] && e.c > e.f)
            {
                d[e.v] = d[e.u] + 1;
                Q.push(e.v);
            }
        }
    }

    return d[t] != 0;
}

int dfs(int u, int cap)
{
//    cout<< u << "  " << cap <<endl;
    if(u == t)
        return cap;
    for(int i=head[u]; i!= -1; i=Node[i].next)
    {
        edge e = Node[i];
        if(d[e.v] == d[e.u] + 1 && e.c > e.f)
        {
            int V = dfs(e.v, min(cap, e.c - e.f));
            if(V > 0){
                Node[i].f += V;
                Node[i^1].f -= V;
                return V;
            }
        }
    }
    return 0;
}
int Dinic()
{
    int ans = 0;
    while(bfs())
    {
        while(int l = dfs(s,INF))
            ans += l;
    }
    return ans;
}


int main()
{
    mem(head,-1);
    cin>> n >> m >> s >> t;
    int cnt = 0;
    for(int i=0; i<m; i++)
    {
        int u, v, w;
        cin>> u >> v >> w;
        add(u, v, w, 0, cnt++);
        add(v, u, 0, 0, cnt++);
    }
    cout<< Dinic() <<endl;

    return 0;
}