hdu6118(费用流模版)

题目：hdu6118
裸的最小费用流模版，记录一下
代码如下：

#include <cstdio>
#include <algorithm>
#include <cstring>
#include <queue>

using namespace std;

const int maxn = 500 + 10;
const int maxm = 4000 + 10;
const int INF = (int)1e9;

int lst[maxn], nxt[2*maxm], to[2*maxm], c[2*maxm], f[2*maxm];
int in[maxn], dis[maxn];
int n, m, s, t, ans, cnt;


void add(int u, int v, int w, int fw) {
    nxt[++cnt] = lst[u]; lst[u] = cnt; to[cnt] = v; c[cnt] = w; f[cnt] = fw;
    nxt[++cnt] = lst[v]; lst[v] = cnt; to[cnt] = u; c[cnt] = -w; f[cnt] = 0;
}

queue<int> Q;
int pre[maxn];

bool spfa(){
    for (int i = 1; i <= t; i ++) dis[i] = INF;
    memset(pre, 0, sizeof(pre));
    memset(in, 0, sizeof(in));
    Q.push(s);
    dis[s] = 0;

    while (!Q.empty()) {
    int u = Q.front(); Q.pop();
    in[u] = 0;
    for (int j = lst[u]; j; j = nxt[j]) {
        int v = to[j];
        if (!f[j]) continue;
        if (dis[u] + c[j] < dis[v]) {
        dis[v] = dis[u] + c[j];
        pre[v] = j;

        if (!in[v]) {
            in[v] = 1;
            Q.push(v);
        }
        }
    }
    }
    return dis[t] < 0;
}

void update(){
    int now = t, fw = INF;
    while (now != s) {
    int kk = pre[now];
    if (f[kk] < fw) fw = f[kk];
    now = to[kk^1];
    }
    ans -= fw * dis[t];
    now = t;
    while (now != s) {
    int kk = pre[now];
    f[kk] -= fw;
    f[kk^1] += fw;
    now = to[kk^1];
    }
}

int main(){
    freopen("a.in", "r", stdin);
    freopen("a.out", "w", stdout);

    while (scanf("%d %d", &n, &m) == 2) {
    memset(lst, 0, sizeof(lst)); cnt = 1;
    memset(nxt, 0, sizeof(nxt));
    s = n + 1; t = s + 1;

    for (int i = 1; i <= n; i ++) {
        int a, b, cc, d;
        scanf("%d %d %d %d", &a, &b, &cc, &d);
        add(s, i, a, b);
        add(i, t, -cc, d);
    }
    for (int i = 1; i <= m; i ++) {
        int a, b, w;
        scanf("%d %d %d", &a, &b, &w);
        add(a, b, w, INF);
        add(b, a, w, INF);
    }
    ans = 0;
    while (spfa()) update();
    printf("%d\n", ans);    
    }

    return 0;
}