题意:找出所有出度为0的连通分支
AC代码
#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<cstdio>
#include<queue>
#include<stack>
#include<map>
#include<stdlib.h>
#include<set>
#include<vector>
using namespace std;
#define CLR(a,b) memset(a,b,sizeof(a))
#define INF 0x3f3f3f3f
#define LL long long
#define Pi acos(-1.0)
#define EXP 1e-9
#define up(i,x,y) for(int i=x;i<=y;i++)
#define down(i,x,y) for(int i=x;i>=y;i--)
#define w(x) while(x)
#define Mod 1000000007
struct node{
int next;
int v;
}edge[50100];
int dfn[50100];
int low[50100];
int head[50100];
int astack[50100];
int vis[50100];
int astacknum=0;
int cnt=0;
int tot=0;
int belongs[50100];
int belongsnum=0;
int a[50100];
int b[50100];
int out[50100];
void add(int x,int y)
{
edge[++cnt].next=head[x];
edge[cnt].v=y;
head[x]=cnt;
return ;
}
void tarjan(int x)
{
dfn[x]=low[x]=++tot;
astack[++astacknum]=x;
vis[x]=1;
for(int i=head[x];i!=-1;i=edge[i].next){
if(!dfn[edge[i].v]){
tarjan(edge[i].v);
low[x]=min(low[x],low[edge[i].v]);
}
else if(vis[edge[i].v])
low[x]=min(low[x],dfn[edge[i].v]);
}
if(low[x]==dfn[x]){
belongsnum++;
do{
belongs[astack[astacknum]]=belongsnum;
vis[astack[astacknum]]=0;
astacknum--;
}while(x!=astack[astacknum+1]);
}
return ;
}
void init()
{
CLR(dfn,0);
CLR(low,0);
CLR(out,0);
cnt=0;
tot=0;
CLR(belongs,0);
belongsnum=0;
CLR(astack,0);
astacknum=0;
CLR(vis,0);
CLR(head,-1);
return ;
}
int main()
{
int v,e;
while(cin>>v){
if(v==0)
break;
cin>>e;
init();
for(int i=1;i<=e;i++){
cin>>a[i]>>b[i];
add(a[i],b[i]);
}
for(int i=1;i<=v;i++){
if(!dfn[i]) tarjan(i);
}
for(int i=1;i<=e;i++){
if(belongs[a[i]]!=belongs[b[i]]){
out[belongs[a[i]]]++;
}
}
int flag=0;
for(int i=1;i<=v;i++){
if(out[belongs[i]]==0){
if(!flag){
cout<<i;
flag=1;
}
else
cout<<" "<<i;
}
}
cout<<endl;
}
return 0;
}