ACM/ICPC 之 电力网络-EK算法(POJ1459)

　　按照电站发电（从源点到电站），消费者消费（从消费者到汇点）的想法构建网络，以下是EK解法

//网络流EK算法
//Time:922Ms    memory:224K
#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<queue>
using namespace std;

#define MAX 105
#define INF 0x3f3f3f3f

int n,np,nc,m;
int s,t;
int res[MAX][MAX];  //残留网络
int pre[MAX];

bool bfs()
{
    memset(pre,-1,sizeof(pre));
    queue<int> q;
    q.push(s);  pre[s] = 0;
    while(!q.empty()){
        int cur = q.front();
        q.pop();
        for(int i = 1; i <= t; i++)
        {
            if(pre[i] == -1 && res[cur][i])
            {
                pre[i] = cur;
                if(i == t) return true;
                q.push(i);
            }
        }
    }
    return false;
}

int EK()
{
    int maxFlow = 0;
    while(bfs()){
        int alpha = INF;    //最小可改进量
        for(int i = t; i != s; i = pre[i])
            alpha = min(alpha, res[pre[i]][i]);
        for(int i = t; i != s; i = pre[i])
        {
            res[pre[i]][i] -= alpha;
            res[i][pre[i]] += alpha;
        }
        maxFlow += alpha;
    }
    return maxFlow;
}

int main()
{
	//freopen("in.txt", "r", stdin);

	while(~scanf("%d%d%d%d", &n,&np,&nc,&m)){
        s = 0;  t = n+2;
        memset(res,0,sizeof(res));
        int a,b,c;
        while(m--){
            scanf(" (%d,%d)%d", &a,&b,&c);
            res[a+1][b+1] = c;
        }
        for(int i = 0; i < np; i++)
        {   //电站
            scanf(" (%d)%d", &b,&c);
            res[s][b+1] = c;
        }
        for(int i = 0; i < nc; i++)
        {   //消费
            scanf(" (%d)%d", &a,&c);
            res[a+1][t] = c;
        }

        printf("%d
", EK());

	}

	return 0;
}