bzoj千题计划161：bzoj1589: [Usaco2008 Dec]Trick or Treat on the Farm 采集糖果

http://www.lydsy.com/JudgeOnline/problem.php?id=1589

 

tarjan缩环后拓扑排序上DP

 

#include<cstdio>
#include<iostream>
#include<algorithm>

#define N 100001

using namespace std;

int to[N];

int m;
int bl[N],siz[N];

int st[N],top;
int id,dfn[N],low[N];
bool vis[N];

int FRONT[N],TO[N],NXT[N],TOT;
int in[N];

int dp[N];

void read(int &x)
{
    x=0; char c=getchar();
    while(!isdigit(c)) c=getchar();
    while(isdigit(c)) { x=x*10+c-'0'; c=getchar(); }
}

void tarjan(int x)
{
    dfn[x]=low[x]=++id;
    vis[x]=true;
    st[++top]=x;
    if(!dfn[to[x]])
    {
        tarjan(to[x]);
        low[x]=min(low[x],low[to[x]]);
    }
    else if(vis[to[x]]) low[x]=min(low[x],dfn[to[x]]);
    if(dfn[x]==low[x])
    {
        ++m;
        while(st[top]!=x) 
        {
            vis[st[top]]=false;
            bl[st[top]]=m;
            siz[m]++;
            top--;
        }
        vis[x]=false;
        bl[x]=m;
        siz[m]++;
        top--;
    }
}

void add(int u,int v)
{
    TO[++TOT]=v; NXT[TOT]=FRONT[u]; FRONT[u]=TOT;
    in[v]++;
}

void topsort()
{
    top=0;
    for(int i=1;i<=m;++i)
    {
        if(!in[i]) st[++top]=i;
        dp[i]=siz[i];
    } 
    int now,t;
    while(top)
    {
        now=st[top--];
        for(int i=FRONT[now];i;i=NXT[i])
        {
            t=TO[i];
            dp[t]+=dp[now];
            in[t]--;
            if(!in[t]) st[++top]=t;
        }
    }
}

int main()
{
    int n;
    read(n);
    for(int i=1;i<=n;++i) read(to[i]);
    for(int i=1;i<=n;++i)
        if(!dfn[i]) tarjan(i);
    for(int i=1;i<=n;++i)
        if(bl[i]!=bl[to[i]]) add(bl[to[i]],bl[i]);
    topsort();
    for(int i=1;i<=n;++i) cout<<dp[bl[i]]<<'\n';
}

 

转载于:https://www.cnblogs.com/TheRoadToTheGold/p/8142648.html