C++ :

#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
const int N=50000;
struct node{int id,k,a;}t[N+1];
int f[N+1],l[N+1],r[N+1],d[N+1];
int i,n;
bool cmp(node x,node y){return x.k<y.k;}
void build()
{
	int k,top=-1;
	for(i=1;i<=n;i++)
	{
		k=top;
		while(k>=0&&t[d[k]].a>t[i].a)
			k--;
		if(k!=-1)
		{
			f[t[i].id]=t[d[k]].id;
			r[t[d[k]].id]=t[i].id;
		}
		if(k<top)
		{
			f[t[d[k+1]].id]=t[i].id;
			l[t[i].id]=t[d[k+1]].id;
		}
		d[++k]=i;
		top=k;
	}
}
int main()
{
	while(~scanf("%d",&n))
	{
		memset(f,0,sizeof(f));
		memset(l,0,sizeof(l));
		memset(r,0,sizeof(r));
		for(i=1;i<=n;i++)
			scanf("%d%d",&t[i].k,&t[i].a),t[i].id=i;
		sort(t+1,t+n+1,cmp);
		build();
		printf("yes\n");
		for(i=1;i<=n;i++)
			printf("%d %d %d\n",f[i],l[i],r[i]);
	}
	return 0;
}

Pascal :

program p26935;
var k:array[0..50000]of longint;
    w:array[0..50000]of longint;
    a:array[0..50000]of longint;
    ans:array[0..50000,1..3]of longint;
    i,j,t,n,now,total:longint;
procedure qsort(l,r:longint);
var i,j,x,y:longint;
begin
  x:=k[(l+r)div 2];
  i:=l;j:=r;
  repeat
  while k[i]<x do inc(i);
  while k[j]>x do dec(j);
  if i<=j then
    begin
      t:=k[i];k[i]:=k[j];k[j]:=t;
      t:=w[i];w[i]:=w[j];w[j]:=t;
      t:=a[i];a[i]:=a[j];a[j]:=t;
      inc(i);dec(j);
    end;
  until i>j;
  if i<r then qsort(i,r);
  if j>l then qsort(l,j);
end;{qsort}
begin{main}
  readln(n);
  for i:=1 to n do
    begin
      readln(k[i],a[i]);
      w[i]:=i;
    end;
  qsort(1,n);
  ans[1,1]:=0;
  ans[1,2]:=0;
  ans[1,3]:=0;
  now:=1;
  for i:=2 to n do
    begin
      while (a[i]<a[now])and(ans[now,1]<>0) do
        now:=ans[now,1];
      if a[i]<a[now] then
        begin
          ans[now,1]:=i;
          ans[i,2]:=now;
        end
      else
        begin
          if ans[now,3]<>0 then begin
            ans[i,2]:=ans[now,3];
            ans[ans[now,3],1]:=i;
            end;
          ans[now,3]:=i;
          ans[i,1]:=now;
        end;
      now:=i;
    end;
  total:=1;
  for i:=1 to n do
    if ans[i,1]<>0 then inc(total);
  if total=n then
    begin
      writeln('yes');
      for i:=1 to n do
        for j:=1 to n do
          begin
           if w[j]=i then
             writeln(w[ans[j,1]],' ',w[ans[j,2]],' ',w[ans[j,3]]);
          end;
    end
  else  writeln('no');
end.