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;

}