hdu 3549 Flow Problem

网络流的基础题，EK算法模板，留着...

 

#include <iostream>
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <vector>
#include <set>
#include <queue>
#include <stack>
#include <climits>
#define MAX 20
#define INF 0x7FFFFFFF
# define eps 1e-5
//#pragma comment(linker, "/STACK:36777216") ///传说中的外挂
using namespace std;

int cap[MAX][MAX],flow[MAX],pre[MAX];
int n,m;

void init()
{
    memset(cap,0,sizeof(cap));
    memset(flow,0,sizeof(flow));
}

int bfs(int s,int e)
{
    queue<int >q;
    memset(pre,-1,sizeof(pre));
    pre[s] = 0;
    flow[s] = INF;
    q.push(s);
    while(! q.empty())
    {
        int t = q.front();
        q.pop();
        if(t == e)
            break;
        for(int i=1; i<=n; i++)
        {
            if(i != s && cap[t][i] > 0 && pre[i] == -1) // 相连且未被访问过
            {
                pre[i] = t;
                flow[i] = min(cap[t][i],flow[t]); // 更新该点的改进流量
                q.push(i);
            }
        }
    }
    if(pre[e] == -1)
        return -1;
    else
        return flow[e];
}

int maxflow(int s,int e)
{
    int aug = 0;
    int sumflow = 0;
    while((aug = bfs(s,e)) != -1) //每一次找出残余流量
    {
        int ind = e;//利用pre来找前驱结点
        while(ind != s)
        {
            cap[pre[ind]][ind] -= aug;
            cap[ind][pre[ind]] += aug;
            ind = pre[ind];
        }
        sumflow += aug;
    }
    return sumflow;
}

int main()
{
    int tt = 1;
    int t,a,b,c;
    cin >> t;
    while(t --)
    {
        init();
        scanf("%d%d",&n,&m);
        for(int i=0; i<m; i++)
        {
            scanf("%d%d%d",&a,&b,&c);
            if(a == b)
                continue;
            cap[a][b] += c;
        }
        printf("Case %d: ",tt++);
        printf("%d\n",maxflow(1,n));
    }
    return 0;
}