ZOJ 3795 Grouping 强联通缩点+拓扑序+偏序集的最大链的大小

#include<iostream>
#include<string.h>
#include<stdlib.h>
#include<stdio.h>
#include<queue>
#include<algorithm>
using namespace std;
const int MAXN = 100010; //点数
const int MAXM = 300010; //边数
struct Edge
{
    int to, next;
} edge[MAXM];
int head[MAXN],tot;
int Low[MAXN],DFN[MAXN],Stack[MAXN],Belong[MAXN]; //Belong数组的值是1~scc
int Index,top;
int scc; //强连通分量的个数
bool Instack[MAXN];
int num[MAXN]; //各个强连通分量包含点的个数，数组编号1~scc
//num数组不一定需要，结合实际情况
int dis[MAXN];
int in[MAXN];
vector<int>G[MAXN];
void addedge(int u, int v)
{
    edge[tot]. to = v;
    edge[tot]. next = head[u];
    head[u] = tot++;
}
void Tarjan( int u)
{
    int v;
    Low[u] = DFN[u] = ++Index;
    Stack[top++] = u;
    Instack[u] = true;
    for(int i = head[u]; i != - 1; i = edge[i]. next)
    {
        v = edge[i]. to;
        if( !DFN[v] )
        {
            Tarjan(v);
            if( Low[u] > Low[v] )Low[u] = Low[v];
        }
        else if(Instack[v] && Low[u] > DFN[v])
            Low[u] = DFN[v];
    }
    if(Low[u] == DFN[u])
    {
        scc++;
        do
        {
            v = Stack[-- top];
            Instack[v] = false;
            Belong[v] = scc;
            num[scc]++;
        }
        while( v != u);
    }
}

void solve(int N)
{
    memset(DFN,0, sizeof(DFN));
    memset(Instack, false, sizeof(Instack));
    memset(num,0,sizeof(num));
    Index = scc = top = 0;
    for(int i = 1; i <= N; i++)
        if(!DFN[i])
            Tarjan(i);
}

void work(){
    memset(dis,0,sizeof(dis));
    queue<int>q;
    for(int i=1;i<=scc;i++){
        if(in[i]==0) {q.push(i);dis[i]=num[i];}
    }
    while(!q.empty()){
        int u=q.front();
        q.pop();
        int v;
        for(int i=0;i<G[u].size();i++){
            v=G[u][i];
            dis[v]=max(dis[u]+num[v],dis[v]);
            in[v]--;
            if(in[v]==0) q.push(v);
        }
    }
    int ans=0;
    for(int i=1;i<=scc;i++){
        ans=max(ans,dis[i]);
    }
    printf("%d\n",ans);
}

void init()
{
    tot = 0;
    memset(head, -1, sizeof(head));
    memset(in,0,sizeof(in));
}

int main(){
    int n,m,a,b;
    while(~scanf("%d%d",&n,&m)){
        init();
        for(int i=1;i<=m;i++){
            scanf("%d%d",&a,&b);
            addedge(a,b);
        }
        solve(n);
        for(int i=1;i<=scc;i++){
            G[i].clear();
        }
        for(int i=1;i<=n;i++){
            for(int j=head[i];j!=-1;j=edge[j].next)
            {
                int v=edge[j].to;
                if(Belong[i]!=Belong[v]){
                        in[Belong[v]]++;
                        G[Belong[i]].push_back(Belong[v]);
                }
            }
        }
        work();
    }
return 0;
}

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