最大流

还是比较好理解的，看大白后一下就理解了，注释也写得很详细了，直接上模板吧

#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#include <queue>

using namespace std;

#define MAXN 30
#define INF 1e8

struct Edge
{
    int from,to,cap,flow;
    Edge(int fr,int t,int c,int f):from(fr),to(t),cap(c),flow(f){}
};

int n,real_m,m; //n个点，m条边
vector<Edge> edges; //所有的边
vector<int> G[MAXN]; //G[i][j]表示 起点 i 的第 j 条边的序号
int add[MAXN]; //可增量
int pre[MAXN]; //前驱

void Init()
{
    edges.clear();
    for(int i=0;i<=n;i++)
        G[i].clear();
}

int AddEdge(int from,int to,int cap)
{
    edges.push_back(Edge(from,to,cap,0));
    edges.push_back(Edge(to,from,0,0));
    m=edges.size();
    G[from].push_back(m-2);
    G[to].push_back(m-1);
    return 0;
}

int MaxFlow(int s,int t)
{
    int flow=0;
    while(1)
    {
        memset(add,0,sizeof(add));

        add[s]=INF;
        queue<int> Q;
        Q.push(s);

        while(!Q.empty())
        {
            int u = Q.front(); Q.pop();
            for(int i=0;i<G[u].size();i++)
            {
                Edge e = edges[G[u][i]];
                if(!add[e.to]&&e.cap>e.flow)//如果没去过并且可增
                {
                    add[e.to]=min(add[u],e.cap-e.flow);
                    pre[e.to]=G[u][i];
                    Q.push(e.to);
                }
                if(add[t])
                    break;
            }
        }
        if (!add[t]) //不能增了
            break;

        for(int u=t;u!=s;u=edges[pre[u]].from)
        {
            int num=pre[u];//那条边的编号
            edges[num].flow +=add[t];
            edges[num^1].flow-=add[t];
        }
        flow+=add[t];
    }
    return flow;
}

int main()
{
    while(1)
    {
        cout<<"输入顶点个数:"; cin >> n;
        Init();

        int from , to ,cap;
        cout<<"输入边个数:"; cin>>real_m;
        cout<<"起点 终点 容量"<<endl;
        for(int i=0;i<real_m;i++)
        {
            scanf("%d%d%d",&from,&to,&cap);
            AddEdge(from,to,cap);
        }
        int s,t;
        cout<<"起点:"; cin >> s;
        cout<<"终点:"; cin >> t;
        cout<<"最大流量为:"<<MaxFlow(s,t)<<endl;
    }
    return 0;
}