Problem:
Score : 100 points

Problem Statement

You are given a directed graph with N vertices and M edges, not necessarily simple. The i-th edge is oriented from the vertex a_i to the vertex b_i.
Divide this graph into strongly connected components and print them in their topological order.

Constraints

1 \leq N \leq 500,000

1 \leq M \leq 500,000

0 \leq a_i, b_i < N

Input

Input is given from Standard Input in the following format:

N M
a_0 b_0
a_1 b_1
:
a_{M - 1} b_{M - 1}

Output

Print 1+K lines, where K is the number of strongly connected components.
Print K on the first line.
Print the information of each strongly connected component in next K lines in the following format, where l is the number of vertices in the strongly connected component and v_i is the index of the vertex in it.

l v_0 v_1 ... v_{l-1}

Here, for each edge (a_i, b_i), b_i should not appear in earlier line than a_i.

If there are multiple correct output, print any of them.

Sample Input 1

6 7
1 4
5 2
3 0
5 5
4 1
0 3
4 2

Sample Output 1

4
1 5
2 4 1
1 2
2 3 0

Solution in Perl (5.26.1) (judge verdict: Accepted)

package scc;
sub new{
	return bless[map[],1..$_[1]],$_[0];
}
sub add_edge{
	my$self=shift;
	push@{$self->[$_[0]]},$_[1];
}
sub scc{
	my$self=shift;
	my$now_ord=0,$group_num=0,@low,@ord=(-1)x@{$self},@ids;
	my@visited;
	my$dfs;
	$dfs=sub{
		my$v=shift;
		$low[$v]=$ord[$v]=$now_ord++;
		push@visited,$v;
		for$to(@{$self->[$v]}){
			if($ord[$to]==-1){
				$dfs->($to);
				$low[$v]=$low[$to]if$low[$v]>$low[$to];
			}
			else{
				$low[$v]=$ord[$to]if$low[$v]>$ord[$to];
			}
		}
		if($low[$v]==$ord[$v]){
			my$u=-1;
			while($u!=$v){
				$u=pop@visited;
				$ord[$u]=@{$self};
				$ids[$u]=$group_num;
			}
			$group_num++;
		}
	};
	for$i(0..$#ord){
		$dfs->($i)if$ord[$i]==-1;
	}
	$_=$group_num-1-$_ for@ids;
	my@groups=map[],1..$group_num;
	for$i(0..$#ids){
		push@{$groups[$ids[$i]]},$i;
	}
	return\@groups;
}
package main;
my($N,$M)=split$",<>;
my$scc=scc->new($N);
for(1..$M){
	my($a,$b)=split$",<>;
	$scc->add_edge($a,$b);
}
$groups=$scc->scc();
print scalar(@{$groups}),$/;
for$L(@{$groups}){
	print scalar(@{$L}),$","@{$L}",$/;
}