ZJU 3362 Beer Problem

赤裸裸的最小费用流

 

/* 
 * File:   ZJU 3362 Beer Problem
 * Author: xiaotian @ hnu
 * Created on 2010年10月30日, 下午12:05
 * 解题：
 */

#include<iostream>
#include<queue>
#include<stdio.h>
#include<string.h>
using namespace std;
const int N = 105;
const int E = 8100;
const int inf = 0x7ffffff;
int mincost, maxflow;
int n, m;
int U[E], V[E], cap[E], flow[E], cost[E], next[E];
int head[N], pre[N], Edge[N], dis[N];
int e;

void addEdge(int u, int v, int Cap, int Cost)
{
    flow[e] = flow[e + 1] = 0;
    V[e] = v; U[e] = u; cap[e] = Cap; cost[e] = Cost;
    next[e] = head[u]; head[u] = e++;
    V[e] = u; U[e] = v; cap[e] = 0; cost[e] = -Cost;
    next[e] = head[v]; head[v] = e++;
}

void MCMF(int st, int ed) {
    queue<int> q;
    memset(flow, 0, sizeof (flow));
    mincost = maxflow = 0;
    for (;;) {
        bool inq[N];
        for (int i = st; i <= ed; ++i)
            dis[i] = (i == st ? 0 : inf);
        memset(inq, 0, sizeof (inq));
        q.push(st);
        while (!q.empty()) {
            int u = q.front();
            q.pop();
            inq[u] = 0;
            for (int e = head[u]; e != -1; e = next[e]) {
                if (cap[e] > flow[e] && dis[u] + cost[e] < dis[V[e]]) {
                    dis[V[e]] = dis[u] + cost[e];
                    pre[V[e]] = U[e];
                    Edge[V[e]] = e;
                    if (!inq[V[e]]) {
                        q.push(V[e]);
                        inq[V[e]] = 1;
                    }
                }
            }
        }
        if (dis[ed] >= 0) break;
        int delta = inf;
        for (int u = ed; u != st; u = pre[u])
            delta = min(delta, cap[Edge[u]] - flow[Edge[u]]);
        for (int u = ed; u != st; u = pre[u]) {
            flow[Edge[u]] += delta;
            flow[Edge[u] ^ 1] -= delta;
        }
        mincost += dis[ed] * delta;
        maxflow += delta;
    }
}

void build() {
    int u, v, Cap, Cost;
    e = 0;
    memset(head, -1, sizeof (head));
    for (int i = 2; i <= n; ++i) {
        scanf("%d", &Cost);
        addEdge(i, n + 1, inf, -Cost);
    }
    while (m--) {
        scanf("%d%d%d%d", &u, &v, &Cap, &Cost);
        addEdge(u, v, Cap, Cost);
        addEdge(v, u, Cap, Cost);
    }
}

int main() {
    freopen("newfile", "r", stdin);
    while (scanf("%d%d", &n, &m) != EOF) {
        build();
        MCMF(1, n + 1);
        printf("%d\n", -mincost);
    }
    return 0;
}