网络流24题 洛谷 3254 圆桌问题

Posted 2020-11-01 horsepower2001

注意用当前弧优化！

#include<queue>
#include<cstdio>
#include<cstring>
#include<algorithm>
const int MAXN=1e5+5;
const int INF=1e9+7;
int n,m;
struct Edge
{
    int nxt;
    int to;
    int f;
}edge[MAXN<<1];
int num=1,sink,src;
int head[MAXN];
void add(int from,int to,int f)
{
    edge[++num].nxt=head[from];
    edge[num].to=to;
    edge[num].f=f;
    head[from]=num;
    edge[++num].nxt=head[to];
    edge[num].to=from;
    edge[num].f=0;
    head[to]=num;
}
int dist[MAXN];
bool vis[MAXN];
bool bfs()
{
    std::queue<int>q;
    std::memset(dist,0,sizeof(dist));
    std::memset(vis,0,sizeof(vis));
    q.push(src);
    dist[0]=0;
    vis[src]=1;
    while(!q.empty())
    {
        int u=q.front();
        q.pop();
        for(int i=head[u];i;i=edge[i].nxt)
        {
            int v=edge[i].to;
            if(!vis[v]&&edge[i].f)
            {
                dist[v]=dist[u]+1;
                q.push(v);
                vis[v]=1;
            }
        }
    }
    return vis[sink];
}
int maxflow(int x,int delta)
{
    if(x==sink)
    {
        return delta;
    }
    int res=0;
    for(int i=head[x];i && delta;i=edge[i].nxt)
    {
        int v=edge[i].to;
        if(dist[v]==dist[x]+1&&edge[i].f)
        {
            int dd=maxflow(v,std::min(edge[i].f,delta));
            res+=dd;
            delta-=dd;
            edge[i].f-=dd;
            edge[i^1].f+=dd;
        }
    }
    return res;
}
int ans=0;
void dinic()
{
    while(bfs())
    {
        ans+=maxflow(src,INF);
    }
}
int q[MAXN];
void print()
{
    for(int i=1;i<=n;i++)
    {
        q[0]=0;
        std::memset(q,0,sizeof(q));
        for(int j=head[i];j;j=edge[j].nxt)
        {
            int v=edge[j].to;
            if(!edge[j].f)
            {
                q[++q[0]]=v-n;
            }
        }
        for(int k=q[0];k>0;k--)
        {
            printf("%d ",q[k]);
        }
        printf("\n");
    }
}
int main()
{
    int sum=0;
    std::scanf("%d%d",&n,&m);
    sink=n+m+1;
    src=0;
    for(int i=1;i<=n;i++)
    {
        int x;
        std::scanf("%d",&x);
        add(src,i,x);
        for(int j=n+1;j<=n+m;j++)
        {
            add(i,j,1);
        }
        sum+=x;
    }
    for(int i=n+1;i<=m+n;i++)
    {
        int x;
        std::scanf("%d",&x);
        add(i,sink,x);
    }
    dinic();
    if(ans==sum)
    {
        printf("1\n");
        print();
    }
    else 
    printf("0\n");
    return 0;
}

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