zoukankan      html  css  js  c++  java
  • poj 2186 Popular Cows tarjan

    Popular Cows

    Description

    Every cow's dream is to become the most popular cow in the herd. In a herd of N (1 <= N <= 10,000) cows, you are given up to M (1 <= M <= 50,000) ordered pairs of the form (A, B) that tell you that cow A thinks that cow B is popular. Since popularity is transitive, if A thinks B is popular and B thinks C is popular, then A will also think that C is 
    popular, even if this is not explicitly specified by an ordered pair in the input. Your task is to compute the number of cows that are considered popular by every other cow. 

    Input

    * Line 1: Two space-separated integers, N and M 

    * Lines 2..1+M: Two space-separated numbers A and B, meaning that A thinks B is popular. 

    Output

    * Line 1: A single integer that is the number of cows who are considered popular by every other cow. 

    Sample Input

    3 3
    1 2
    2 1
    2 3
    

    Sample Output

    1
    

    Hint

    Cow 3 is the only cow of high popularity. 
    low数组的理解:对于一个点,能从未遍历的边到达的最低的深度优先级
    #include<iostream>
    #include<cstdio>
    #include<cmath>
    #include<string>
    #include<queue>
    #include<algorithm>
    #include<stack>
    #include<cstring>
    #include<vector>
    #include<list>
    #include<set>
    #include<map>
    using namespace std;
    #define ll __int64
    #define inf 2000000001
    int scan()
    {
        int res = 0 , ch ;
        while( !( ( ch = getchar() ) >= '0' && ch <= '9' ) )
        {
            if( ch == EOF )  return 1 << 30 ;
        }
        res = ch - '0' ;
        while( ( ch = getchar() ) >= '0' && ch <= '9' )
            res = res * 10 + ( ch - '0' ) ;
        return res ;
    }
    struct is
    {
        int u,v;
        int next;
    }edge[50010];
    int head[50010];
    int belong[50010];
    int dfn[50010];
    int low[50010];
    int stackk[50010];
    int instack[50010];
    int number[50010];
    int du[100010];
    int n,m,jiedge,lu,bel,top;
    void update(int u,int v)
    {
        jiedge++;
        edge[jiedge].u=u;
        edge[jiedge].v=v;
        edge[jiedge].next=head[u];
        head[u]=jiedge;
    }
    void dfs(int x)
    {
        dfn[x]=low[x]=++lu;
        stackk[++top]=x;
        instack[x]=1;
        for(int i=head[x];i;i=edge[i].next)
        {
            if(!dfn[edge[i].v])
            {
                dfs(edge[i].v);
                low[x]=min(low[x],low[edge[i].v]);
            }
            else if(instack[edge[i].v])
            low[x]=min(low[x],dfn[edge[i].v]);
        }
        if(low[x]==dfn[x])
        {
            int sum=0;
            bel++;
            int ne;
            do
            {
                sum++;
                ne=stackk[top--];
                belong[ne]=bel;
                instack[ne]=0;
            }while(x!=ne);
            number[bel]=sum;
        }
    }
    void tarjan()
    {
        memset(dfn,0,sizeof(dfn));
        bel=lu=top=0;
        for(int i=1;i<=n;i++)
        if(!dfn[i])
        dfs(i);
    }
    int main()
    {
        int i,t;
        while(~scanf("%d%d",&n,&m))
        {
            memset(head,0,sizeof(head));
            jiedge=0;
            for(i=1;i<=m;i++)
            {
                int u,v;
                scanf("%d%d",&u,&v);
                update(u,v);
            }
            tarjan();
            for(i=1;i<=jiedge;i++)
            if(belong[edge[i].v]!=belong[edge[i].u])
            du[belong[edge[i].u]]++;
            int flag=0,pos;
            /*for(i=1;i<=n;i++)
            cout<<belong[i]<<endl;*/
            for(i=1;i<=bel;i++)
            {
                if(!du[i])
                {
                    flag++;
                    pos=i;
                }
            }
            if(flag!=1)
            printf("0
    ");
            else
            printf("%d
    ",number[pos]);
        }
        return 0;
    }
    View Code
  • 相关阅读:
    C# WinForm API 改进单实例运行
    CF1310D Tourism [随机化]
    CF1311E Construct the Binary Tree
    [IOI2018] werewolf 狼人 [kruskal重构树+主席树]
    #6029. 「雅礼集训 2017 Day1」市场 [线段树]
    P5840 [COCI2015]Divljak [AC自动机,链并]
    CF547E Mike and Friends [AC自动机,离线树状数组]
    P5112 FZOUTSY
    CF 150E Freezing with Style [长链剖分,线段树]
    CF1230E Kamil and Making a Stream
  • 原文地址:https://www.cnblogs.com/jhz033/p/5360779.html
Copyright © 2011-2022 走看看