HDU 1532 Drainage Ditches （网络流模板）

#include <iostream>
#include <queue>
#include <stack>
#include <cstdio>
#include <vector>
#include <map>
#include <set>
#include <bitset>
#include <algorithm>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <string>
#include <sstream>
#include <time.h>
#define x first
#define y second
#define pb push_back
#define mp make_pair
#define lson l,m,rt*2
#define rson m+1,r,rt*2+1
#define mt(A,B) memset(A,B,sizeof(A))
using namespace std;
typedef long long LL;
const double PI = acos(-1);
const int N=1e3+10;
const LL mod=1e9+7;
const int inf = 0x3f3f3f3f;
const LL INF=0x3f3f3f3f3f3f3f3fLL;
struct Edge
{
    int from,to,cap,flow;
    Edge(int u,int v,int c,int f):from(u),to(v),cap(c),flow(f) {}
};
struct EK
{
    int n,m;
    vector<Edge> edges;
    vector<int> G[N];
    int a[N],p[N];
    void init(int n)
    {
        for(int i=0; i<n; i++)G[i].clear();
        edges.clear();
    }
    void AddEdge(int from,int to,int cap)
    {
        edges.pb(Edge(from,to,cap,0));
        edges.pb(Edge(to,from,0,0));
        m=edges.size();
        G[from].pb(m-2);
        G[to].pb(m-1);
    }
    int Maxflow(int s,int t)
    {
        int flow=0;
        while(true)
        {
            mt(a,0);
            queue<int> Q;
            Q.push(s);
            a[s]=inf;
            while(!Q.empty())
            {
                int x=Q.front();
                Q.pop();
                for(int i=0; i<G[x].size(); i++)
                {
                    Edge& e =edges[G[x][i]];
                    if(!a[e.to]&&e.cap>e.flow)
                    {
                        p[e.to]=G[x][i];
                        a[e.to]=min(a[x],e.cap-e.flow);
                        Q.push(e.to);
                    }
                }
                if(a[t])break;
            }
            if(!a[t])break;
            for(int u=t; u!=s; u=edges[p[u]].from)
            {
                edges[p[u]].flow+=a[t];
                edges[p[u]^1].flow-=a[t];
            }
            flow+=a[t];
        }
        return flow;
    }
};
int main()
{
#ifdef Local
    freopen("data.txt","r",stdin);
#endif
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n,m,u,v,val;
    while(cin>>n>>m)
    {
        struct EK ans;
        for(int i=0; i<n; i++)
        {
            cin>>u>>v>>val;
            ans.AddEdge(u,v,val);
        }
        cout<<ans.Maxflow(1,m)<<endl;
    }

#ifdef Local
    cerr << "time: " << (LL) clock() * 1000 / CLOCKS_PER_SEC << " ms" << endl;
#endif
}