标签：网络流   图论   bfs   ek   hdu   

题目链接：HDU 3549 Flow Problem

Flow Problem

2
3 2
1 2 1
2 3 1
3 3
1 2 1
2 3 1
1 3 1

Case 1: 1
Case 2: 2

纯求网络最大流，用EK算法就可以实现。

代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
using namespace std;

#define maxn 20
#define INF 0x3f3f3f3f
int ans, s, t, n;
int a[maxn], pre[maxn];
int flow[maxn][maxn];
int cap[maxn][maxn];

void Edmonds_Karp()
{
    queue<int> q;
    memset(flow, 0, sizeof(flow));
    ans = 0;
    while(1)
    {
        memset(a, 0, sizeof(a));
        a[s] = INF;
        q.push(s);
        while(!q.empty())   //bfs找增光路径
        {

            int u = q.front();
            q.pop();
            for(int v = 1; v <= n; v++)
                if(!a[v] && cap[u][v] > flow[u][v])
                {
                    pre[v] = u;
                    q.push(v);
                    a[v] = min(a[u], cap[u][v]-flow[u][v]);
                }
        }
        if(a[t] == 0) break;
        for(int u = t; u != s; u = pre[u])  //改进网络流
        {
            flow[pre[u]][u] += a[t];
            flow[u][pre[u]] -= a[t];
        }
        ans += a[t];
    }
}

int main()
{
    //freopen("hdu_3549.txt", "r", stdin);
    int T, m, u, v, c;
    scanf("%d", &T);
    for(int cas = 1; cas <= T; cas++)
    {
        scanf("%d%d", &n, &m);
        memset(cap, 0, sizeof(cap));
        while(m--)
        {
            scanf("%d%d%d", &u, &v, &c);
            cap[u][v] += c;
        }
        s = 1, t = n;
        Edmonds_Karp();
        printf("Case %d: %d\n", cas, ans);
    }
    return 0;
}

HDU 3549 Flow Problem 网络最大流问题 Edmonds_Karp算法

标签：网络流   图论   bfs   ek   hdu   

原文地址：http://blog.csdn.net/u011439796/article/details/39485465