hdu - 3549 - Flow Problem（最大流）

题意：N个点，M条边的有向图，边有权（容量），求从点1到点N的最大流（2 <= N <= 15, 0 <= M <= 1000，1 <= 每条边的容量 <= 1000）。

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=3549

——>>……练练……

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

using namespace std;

const int maxn = 15 + 10;
const int INF = 0x3f3f3f3f;

int N, M;

struct Edge{
    int u, v, cap, flow;
    Edge(int u = 0, int v = 0, int cap = 0, int flow = 0):
    u(u), v(v), cap(cap), flow(flow){}
};

struct Dinic{
    int m, s, t;
    vector<Edge> edges;
    vector<int> G[maxn];
    int d[maxn];
    bool vis[maxn];
    int cur[maxn];

    void init(){
        edges.clear();
        for(int i = 1; i <= N; i++) G[i].clear();
    }

    void addEdge(int u, int v, int cap){
        edges.push_back(Edge(u, v, cap, 0));
        edges.push_back(Edge(v, u, 0, 0));
        m = edges.size();
        G[u].push_back(m-2);
        G[v].push_back(m-1);
    }

    bool bfs(){
        memset(vis, 0, sizeof(vis));
        queue<int> qu;
        qu.push(s);
        vis[s] = 1;
        d[s] = 0;
        while(!qu.empty()){
            int u = qu.front(); qu.pop();
            int sz = G[u].size();
            for(int i = 0; i < sz; i++){
                Edge& e = edges[G[u][i]];
                if(!vis[e.v] && e.cap > e.flow){
                    d[e.v] = d[u] + 1;
                    vis[e.v] = 1;
                    qu.push(e.v);
                }
            }
        }
        return vis[t];
    }

    int dfs(int u, int a){
        if(u == t || a == 0) return a;
        int sz = G[u].size(), f, flow = 0;
        for(int& i = cur[u]; i < sz; i++){
            Edge& e = edges[G[u][i]];
            if(d[e.v] == d[u] + 1 && (f = dfs(e.v, min(a, e.cap-e.flow))) > 0){
                cur[u] = i;
                e.flow += f;
                edges[G[u][i]^1].flow -= f;
                flow += f;
                a -= f;
                if(!a) break;
            }
        }
        return flow;
    }

    int Maxflow(int s, int t){
        this->s = s;
        this->t = t;
        int flow = 0;
        while(bfs()){
            memset(cur, 0, sizeof(cur));
            flow += dfs(s, INF);
        }
        return flow;
    }
}din;

void read(){
    int X, Y, C;
    scanf("%d%d", &N, &M);
    din.init();
    for(int i = 0; i < M; i++){
        scanf("%d%d%d", &X, &Y, &C);
        din.addEdge(X, Y, C);
    }
}

int main()
{
    int T, kase = 1;
    scanf("%d", &T);
    while(T--){
        read();
        printf("Case %d: %d\n", kase++, din.Maxflow(1, N));
    }
    return 0;
}