hdu Flow Problem （最大流 裸题）

最大流裸题，贴下模版

view code#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <vector>
#include <queue>
using namespace std;
const int INF = 0x3f3f3f3f;
const int maxn = 1000;
int n, m, s, t, cas=1, _;
int pre[maxn], d[maxn], cur[maxn];
bool vis[maxn];

struct Edge
{
    int from, to, cap, flow, p;
    Edge() {}
    Edge(int from, int to, int cap, int flow, int pre):from(from), to(to), cap(cap), flow(flow), p(pre) {}
}e[maxn*maxn];
int ecnt = 0;

void init()
{
    memset(pre, -1, sizeof(pre));
    ecnt = 0;
    s = 1, t = n;
}

bool BFS()
{
    memset(vis, 0, sizeof(vis));
    queue<int > q;
    q.push(s);
    vis[s] = 1; d[s] = 0;
    while(!q.empty())
    {
        int u = q.front(); q.pop();
        for(int i = pre[u]; ~i; i=e[i].p)
        {
            int v = e[i].to;
            if(!vis[v] && e[i].flow<e[i].cap)
            {
                d[v] = d[u] + 1;
                vis[v] = true;
                q.push(v);
            }
        }
    }
    return vis[t];
}

int DFS(int u, int c)
{
    if(u==t || c==0) return c;
    int flow = 0, f;
    for(int &i=cur[u]; ~i; i=e[i].p)
    {
        int v = e[i].to;
        if(d[v]==d[u]+1 && (f=DFS(v, min(c, e[i].cap-e[i].flow)))>0)
        {
            e[i].flow += f;
            e[i^1].flow -= f;
            flow += f;
            c -= f;
            if(c==0) break;
        }
    }
    return flow;
}

int main()
{
//    freopen("in.txt", "r", stdin);
    scanf("%d", &_);
    while(_--)
    {
        scanf("%d%d", &n, &m);
        init();
        int  u, v, w;
        for(int i=0; i<m; i++)
        {
            scanf("%d%d%d", &u, &v, &w);
            e[ecnt] = Edge(u, v, w, 0, pre[u]);
            pre[u] = ecnt++;
            e[ecnt] = Edge(v, u, 0, 0, pre[v]);
            pre[v] = ecnt++;
        }
        int ans = 0;
        while(BFS())
        {
            for(int i=1; i<=n; i++) cur[i] = pre[i];
            ans += DFS(s, INF);
        }
        printf("Case %d: %d\n", cas++, ans);
    }
}