C++ :

#include<iostream>
#include<set>
using namespace std;
int main(){
    int n,m;    cin>>n>>m;
    int father[n+1];  //存父亲下标的数组   双亲表示法
    set<int> CH[n+1]; //为每个节点开一个set   存储它的孩子
	for(int i=1;i<=n;i++) father[i]=-1;
	int x,y;
	for(int i=0;i<m;i++)
	{
		cin>>x>>y;
		father[y]=x;
		CH[x].insert(y);
	}
	for(int i=1;i<=n;i++)
		if(father[i]==-1) cout<<i<<endl;
    int max=0;
	for(int i=1;i<=n;i++)   //扫描一次，统计最大值
        if(CH[i].size()>max) max=CH[i].size();

    for(int i=1;i<=n;i++)
    if(CH[i].size()==max){
        cout<<i<<endl;
        set<int>::iterator it;
        for(it=CH[i].begin();it!=CH[i].end();it++)
            cout<<*it<<' ';
        cout<<endl;
    }
	    //cout<<i<<':'<<CH[i].size()<<endl;
    return 0;
}

Pascal :

program qi26791;
type
 treetype=record
  father:longint;
  num:longint;
  child:array[1..100]of longint;
 end;
var
 tree:array[1..100]of treetype;
 n,m:longint;
procedure  du;
var
 i,j,k,x,y:longint;
begin
 read(n,m);
 for i:= 1 to m do
  begin
   read(x,y);
   tree[y].father:=x;
   inc(tree[x].num);
   tree[x].child[tree[x].num]:=y;
  end;
end;
function root:longint;
var
 i:longint;
begin
 for i:= 1 to n do
  if tree[i].father=0 then
   begin
    root:=i;
    exit;
   end;
end;
function find:longint;
var
 max,k,i,j:longint;
begin
 max:=0; k:=0;
 for i:= 1 to n do
   if tree[i].num>max then
    begin
     k:=i; max:=tree[i].num;
    end;
   writeln(k);
  for i:= 1 to max-1 do write(tree[k].child[i],' ');
  writeln(tree[k].child[max]);
  for i:= 1 to n do
   if (tree[i].num=max)and(i<>k) then
    begin
     writeln(i);
     for j:= 1 to max-1 do write(tree[i].child[j],' ');
     writeln(tree[i].child[max]);
    end;
end;
begin
 du;
 writeln(root);
 find;
end.