最大流(dinic，正向表)模版

喜欢dinic算法，清晰，简洁，高效，优雅。

uva820.

#include <iostream>
#include <cstdio>
#include <string>
#include <vector>
#include <cstring>
#include <utility>
#include <algorithm>
using namespace std;

const int Maxn = 105;
const int Maxm = 30005;
const int inf = 0x1fffffff;

int n, m, s, t, queue[Maxn], lab[Maxn];
int tot, h[Maxn], nxt[Maxm<<1], v[Maxm<<1], res[Maxm<<1];

void addEdge(int a, int b, int c) {
    v[tot] = b; res[tot] = c; nxt[tot] = h[a]; h[a] = tot++;
    v[tot] = a; res[tot] = 0; nxt[tot] = h[b]; h[b] = tot++;
}

bool bfs(int s, int t) {
    int head, tail, u;
    memset(lab, -1, sizeof(lab));
    lab[s] = head = tail =0;
    queue[0] = s;
    while(head <= tail) {
        u = queue[head++];
        for(int i = h[u]; i != -1; i = nxt[i])
            if(res[i]>0 && lab[v[i]]==-1) {
                lab[v[i]] = lab[u] +1;
                queue[++tail] = v[i];
            }
    }
    if(lab[t] != -1)  return  true;
    else  return  false;
}

int dinicDfs(int delta, int u) {
    int sum =0, tmp;
    if(u == t)  return  delta;
    else {
        for(int i = h[u]; i != -1; i = nxt[i])
            if(lab[v[i]]==lab[u]+1 && res[i]>0) {
                tmp = dinicDfs(min(delta, res[i]), v[i]);
                sum += tmp;
                delta -= tmp;
                res[i] -= tmp;
                res[i^1] += tmp;
            }
        return  sum;
    }
}

int maxFlow(int s, int t) {
    int ans =0;
    while(bfs(s, t))
        ans += dinicDfs(inf, s);
    return  ans;
}

int main()
{
    int a, b, c, Case = 0;
    freopen("data.in", "r", stdin);
    while(scanf("%d", &n) != EOF) {
        if(n == 0)  break;
        tot = 0;
        memset(h, -1, sizeof(h));
        scanf("%d%d%d", &s, &t, &m);
        for(int i = 0; i < m; i++) {
            scanf("%d%d%d", &a, &b, &c);
            addEdge(a, b, c);
            addEdge(b, a, c);
        }
        int ans = maxFlow(s, t);
        printf("Network %d\n", ++Case);
        printf("The bandwidth is %d.\n\n", ans);
    }
    return  0;
}