AC日记——[CQOI2009]DANCE跳舞 洛谷 P3153

[CQOI2009]DANCE跳舞

思路：

　　二分+最大流；

代码：

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
#define maxn 505
#define maxm 30005
#define INF 0x3f3f3f3f
int head[maxn],E[maxm],V[maxm],F[maxm],cnt;
int n,k,deep[maxn],que[maxm<<],s,t;
char map[maxn][maxn];
inline void edge_add(int u,int v,int f)
{
    E[++cnt]=head[u],V[cnt]=v,F[cnt]=f,head[u]=cnt;
    E[++cnt]=head[v],V[cnt]=u,F[cnt]=,head[v]=cnt;
}
bool bfs()
{
    for(int i=s;i<=t;i++) deep[i]=-;
    que[]=s,deep[s]=;int h=,tail=,now;
    while(h<tail)
    {
        now=que[h++];
        for(int i=head[now];i;i=E[i])
        {
            if(F[i]&&deep[V[i]]<)
            {
                deep[V[i]]=deep[now]+;
                if(V[i]==t) return true;
                que[tail++]=V[i];
            }
        }
    }
    return false;
}
int flowing(int now,int flow)
{
    if(now==t||flow<=) return flow;
    int oldflow=,pos;
    for(int i=head[now];i;i=E[i])
    {
        if(!F[i]||deep[V[i]]!=deep[now]+) continue;
        pos=flowing(V[i],min(flow,F[i]));
        F[i]-=pos,F[i^]+=pos,flow-=pos,oldflow+=pos;
        if(!flow) return oldflow;
    }
    if(!oldflow) deep[now]=-;
    return oldflow;
}
bool check(int mid)
{
    cnt=;
    for(int i=s;i<=t;i++) head[i]=;
    for(int i=;i<=n;i++) edge_add(s,i,mid),edge_add(i,i+n,k);
    for(int i=n*+;i<=n*;i++) edge_add(i,t,mid),edge_add(i-n,i,k);
    for(int i=;i<=n;i++)
        for(int v=;v<=n;v++)
            if(map[i][v]=='Y') edge_add(i,v+n*,);
            else edge_add(i+n,n*+v,);
    int res=;
    while(bfs()) res+=flowing(s,INF);
    return res==mid*n;
}
int main()
{
    scanf("%d%d",&n,&k),t=n*+;
    for(int i=;i<=n;i++) scanf("%s",map[i]+);
    int l=,r=n,mid,ans=;
    while(l<=r)
    {
        mid=l+r>>;
        if(check(mid)) l=mid+,ans=mid;
        else r=mid-;
    }
    cout<<ans;
    return ;
}