max_flow(Edmond_Karp) 分类： ACM TYPE 2014-09-02 10:47 92人阅读 评论(0) 收藏

    #include <cstdio>
    #include <iostream>
    #include <cstring>
    #include<queue>

    using namespace std;
    const int INF = 0x3fffffff;

    int  g[1005][1005];
    bool vis[1005];

    int m;

    int Edmond_Karp(int s,int t)
    {
        int pre[1005];
        int flow[1005];
        memset(pre,0,sizeof(pre));
        for(int i=0;i<=m;i++)   flow[i] = INF;
        queue<int>q;
        q.push(s);
        while(q.size())
        {
            int v = q.front();
            q.pop();
            for(int i=1;i<=m;i++)
            {
                if(pre[i] || i==v || g[v][i]==0)  continue;
                pre[i] = v;
                flow[i] = min(flow[v],g[v][i]);
                if(i==t)
                {
                    for(int j=t;j!=s;j=pre[j])
                    {
                        g[pre[j]][j]-=flow[t];
                        g[j][pre[j]]+=flow[t];
                    }
                    return flow[t];
                }
                q.push(i);
            }
        }
         return 0;
    }

    int find_flows(int s,int t)
    {
        int f = 0;
        while(1)
        {
            memset(vis,0,sizeof(vis));
            int flow = Edmond_Karp(s,t);
            if(flow == 0)   return f;
            f+=flow;
        }
    }

    int main()
    {
        int a, b, len;
        int s, t, p;
            scanf("%d%d", &m, &p);
            scanf("%d%d",&s,&t);
            memset(g,0,sizeof(g));

            while(p--)
            {
                scanf("%d%d%d", &a, &b, &len);
                g[a][b] += len;
            }
            printf("%d\n", find_flows(s,t));
        return 0;
    }

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