poj 1273 hdu 1532 網絡流最大流 Dinic算法

保存一份最大流模板

題目鏈接：http://acm.hdu.edu.cn/showproblem.php?pid=1532

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

using namespace std;

const int maxn = 405; //這裏如果是邊的話，記得要乘2，因爲有反向邊，不然會有re
const int inf = 0x3f3f3f3f;//這裏可以處理重邊的情況

struct edge
{
    int u, v, c, f, next;
} e[maxn];
int head[maxn], cnt;

void init()
{
    cnt = 0;
    memset(head, -1, sizeof(head));
}

void addedge(int u, int v, int c)
{
    e[cnt].u = u, e[cnt].v = v, e[cnt].f = 0, e[cnt].c = c, e[cnt].next = head[u], head[u] = cnt++;
    e[cnt].u = v, e[cnt].v = u, e[cnt].f = 0, e[cnt].c = 0, e[cnt].next = head[v], head[v] = cnt++;
}

struct Dinic
{
    int s, t;
    bool vis[maxn];
    int d[maxn];

    bool bfs()
    {
        memset(vis, false, sizeof(vis));
        queue<int> q;
        q.push(s);
        vis[s] = true;
        while(!q.empty())
        {
            int u= q.front();
            q.pop();
            for(int i = head[u]; i != -1; i = e[i].next)
            {
                edge &f = e[i];
                if(!vis[f.v] && f.c > f.f)
                {
                    vis[f.v] = true;
                    d[f.v] = d[u] + 1;
                    q.push(f.v);
                }
            }
        }
        return vis[t];
    }

    int dfs(int x, int a)
    {
        if(x == t || a == 0) return a;
        int flow = 0, ans;
        for(int i = head[x]; i != -1; i = e[i].next)
        {
            edge &f = e[i];
            if(d[f.v] == d[x] + 1 && (ans = dfs(f.v, min(a, f.c - f.f))) > 0)
            {
                f.f += ans;
                e[i ^ 1] .f -= ans;
                flow += ans;
                a -= ans;
                if(a == 0)
                    break;
            }
        }
        return flow;
    }

    int maxflow(int s, int t)
    {
        this->s = s, this->t = t;
        int flow = 0;
        while(bfs())
            flow += dfs(s, inf);
        return flow;
    }
};

Dinic d;

int main()
{
    int n, m;
    while(~scanf("%d%d", &n, &m))
    {
        init();
        for(int i = 0; i < n; i++)
        {
            int u, v, c;
            scanf("%d%d%d", &u, &v, &c);
            addedge(u, v, c);
        }
        int ans = d.maxflow(1, m);
        printf("%d\n", ans);
    }
    return 0;
}