Wannafly挑战赛14 --C题（tarjan缩点）

链接： https://www.nowcoder.com/acm/contest/81/C
来源：牛客网

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<vector>
#include<stack>
#define ll long long
using namespace std;

void dis(int a[], int n){
	printf("总数为%d个\n",n); 
	for(int i = 1; i <= n; i++) 	cout<<a[i]<<", ";
	cout<<endl<<"------------------"<<endl;		
}

const int mx = 1e5+10;
int n,m;
vector<int>ma[mx],ans;
stack<int>st;
int dfn[mx],low[mx],belong[mx],res[mx],add,id;
bool vis[mx];
int in[mx];
void tarjan(int u){
	int v,te;
	st.push(u);
	vis[u] = 1;
	dfn[u] = low[u] = ++add;
	for(int i = 0; i < ma[u].size(); i++){
		v = ma[u][i];
		if(!dfn[v]){
			tarjan(v);
			low[u] = min(low[u],low[v]); 
		} 
		else if(vis[v]){
			low[u] = min(low[u],dfn[v]); 
		}
	}
	if(dfn[u]==low[u]){
		id++;
		while(1){
			te = st.top();
			st.pop();
			vis[te] = 0;
			belong[te] = id;
			if(te == u)
				break;
		
		}
	}
}
int main(){
	int u,v;
	scanf("%d%d",&n,&m);
	while(m--){
		scanf("%d%d",&u,&v);
		ma[u].push_back(v);
	}	
	memset(dfn,0,sizeof(dfn));
	memset(vis,0,sizeof(vis));
	memset(in,0,sizeof(in));
	add = id = 0;
	for(int i = 1; i <= n; i++){
		if(!dfn[i])
			tarjan(i);
	}
	
	for(int i = 1; i <= n; i++){
		for(int j = 0; j < ma[i].size(); j++){
			v = ma[i][j];
			if(belong[i] != belong[v])      //belong【v】错写成 v 
				in[belong[v]]++;
		}
	}
	//dis(in,n);
	memset(res,0x3f3f3f,sizeof(res));
	for(int i = 1; i <= n; i++)
		res[belong[i]] = min(res[belong[i]],i);
		
	for(int i = 1; i <= id; i++){     //错写id 
		if(!in[i])
			ans.push_back(res[i]);
	}
	sort(ans.begin(),ans.end());
	cout<<ans.size()<<endl;
	for(int i = 0; i < ans.size(); i++){
		if(i == 0)
			printf("%d",ans[i]);
		else
			printf(" %d",ans[i]);
	}
	cout<<endl; 
//	dis(belong,n);
	return 0;
}