• [poj 3281]最大流+建图很巧妙


    题目链接:http://poj.org/problem?id=3281

    看了kuangbin大佬的思路,还用着kuangbin板子orz   http://www.cnblogs.com/kuangbin/archive/2012/08/21/2649850.html

    #include<cstdio>
    #include<cstring>
    using namespace std;
    
    const int MAXN = 10010;
    const int MAXM = 40010;
    const int INF = 0x3f3f3f3f;
    struct Edge
    {
        int to,next,cap,flow;
    } edge[MAXM];
    int tol;
    int head[MAXN];
    int gap[MAXN],dep[MAXN],pre[MAXN],cur[MAXN];
    void init()
    {
        tol = 0;
        memset(head,-1,sizeof(head));
    }
    void addedge(int u,int v,int w,int rw=0)
    {
        edge[tol].to = v;
        edge[tol].cap = w;
        edge[tol].next = head[u];
        edge[tol].flow = 0;
        head[u] = tol++;
        edge[tol].to = u;
        edge[tol].cap = rw;
        edge[tol].next = head[v];
        edge[tol].flow = 0;
        head[v]=tol++;
    }
    int sap(int start,int end,int N)
    {
        memset(gap,0,sizeof(gap));
        memset(dep,0,sizeof(dep));
        memcpy(cur,head,sizeof(head));
        int u = start;
        pre[u] = -1;
        gap[0] = N;
        int ans = 0;
        while(dep[start] < N)
        {
            if(u == end)
            {
                int Min = INF;
                for(int i = pre[u]; i != -1; i = pre[edge[i^1].to])
                    if(Min > edge[i].cap - edge[i].flow)
                        Min = edge[i].cap - edge[i].flow;
                for(int i = pre[u]; i != -1; i = pre[edge[i^1].to])
                {
                    edge[i].flow += Min;
                    edge[i^1].flow -= Min;
                }
                u = start;
                ans += Min;
                continue;
            }
            bool flag = false;
            int v;
            for(int i = cur[u]; i != -1; i = edge[i].next)
            {
                v = edge[i].to;
                if(edge[i].cap - edge[i].flow && dep[v]+1 == dep[u])
                {
                    flag = true;
                    cur[u] = pre[v] = i;
                    break;
                }
            }
            if(flag)
            {
                u = v;
                continue;
            }
            int Min = N;
            for(int i = head[u]; i != -1; i = edge[i].next)
                if(edge[i].cap - edge[i].flow && dep[edge[i].to] < Min)
                {
                    Min = dep[edge[i].to];
                    cur[u] = i;
                }
            gap[dep[u]]--;
            if(!gap[dep[u]])return ans;
            dep[u] = Min+1;
            gap[dep[u]]++;
            if(u != start) u = edge[pre[u]^1].to;
        }
        return ans;
    }
    
    int main()
    {
        int n,F,D;
        scanf("%d%d%d",&n,&F,&D);
        init();
        for (int i=0;i<n;i++) addedge(i,i+n,1);
        for (int i=0;i<n;i++)
        {
            int f,d;
            scanf("%d%d",&f,&d);
            for (int j=0;j<f;j++)
            {
                int x;
                scanf("%d",&x);
                x--;
                addedge(n+n+x,i,1);
            }
            for (int j=0;j<d;j++)
            {
                int x;
                scanf("%d",&x);
                x--;
                addedge(n+i,n+n+F+x,1);
            }
        }
        for (int i=0;i<F;i++) addedge(n+n+F+D,n+n+i,1);
        for (int i=0;i<D;i++) addedge(n+n+F+i,n+n+F+D+1,1);
        printf("%d",sap(n+n+F+D,n+n+F+D+1,n+n+F+D+2));
        return 0;
    }
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  • 原文地址:https://www.cnblogs.com/acmsong/p/7462143.html
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