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 Rust (1.42.0) (judge verdict: Accepted)

#![allow(unused_imports)]
#![allow(non_snake_case, unused)]

use std::cmp::*;
use std::collections::*;
use std::ops::*;

// https://atcoder.jp/contests/hokudai-hitachi2019-1/submissions/10518254 より

macro_rules! eprint {
    ($($t:tt)*) => {{
        use ::std::io::Write;
        let _ = write!(::std::io::stderr(), $($t)*);
    }};
}
macro_rules! eprintln {
    () => { eprintln!(""); };
    ($($t:tt)*) => {{
        use ::std::io::Write;
        let _ = writeln!(::std::io::stderr(), $($t)*);
    }};
}
macro_rules! dbg {
    ($v:expr) => {{
        let val = $v;
        eprintln!("[{}:{}] {} = {:?}", file!(), line!(), stringify!($v), val);
        val
    }}
}

macro_rules! mat {
    ($($e:expr),*) => { Vec::from(vec![$($e),*]) };
    ($($e:expr,)*) => { Vec::from(vec![$($e),*]) };
    ($e:expr; $d:expr) => { Vec::from(vec![$e; $d]) };
    ($e:expr; $d:expr $(; $ds:expr)+) => { Vec::from(vec![mat![$e $(; $ds)*]; $d]) };
}

macro_rules! ok {
    ($a:ident$([$i:expr])*.$f:ident()$(@$t:ident)*) => {
        $a$([$i])*.$f($($t),*)
    };
    ($a:ident$([$i:expr])*.$f:ident($e:expr$(,$es:expr)*)$(@$t:ident)*) => { {
        let t = $e;
        ok!($a$([$i])*.$f($($es),*)$(@$t)*@t)
    } };
}

pub fn readln() -> String {
    let mut line = String::new();
    ::std::io::stdin().read_line(&mut line).unwrap_or_else(|e| panic!("{}", e));
    line
}

macro_rules! read {
    ($($t:tt),*; $n:expr) => {{
        let stdin = ::std::io::stdin();
        let ret = ::std::io::BufRead::lines(stdin.lock()).take($n).map(|line| {
            let line = line.unwrap();
            let mut it = line.split_whitespace();
            _read!(it; $($t),*)
        }).collect::<Vec<_>>();
        ret
    }};
    ($($t:tt),*) => {{
        let line = readln();
        let mut it = line.split_whitespace();
        _read!(it; $($t),*)
    }};
}

macro_rules! _read {
    ($it:ident; [char]) => {
        _read!($it; String).chars().collect::<Vec<_>>()
    };
    ($it:ident; [u8]) => {
        Vec::from(_read!($it; String).into_bytes())
    };
    ($it:ident; usize1) => {
        $it.next().unwrap_or_else(|| panic!("input mismatch")).parse::<usize>().unwrap_or_else(|e| panic!("{}", e)) - 1
    };
    ($it:ident; [usize1]) => {
        $it.map(|s| s.parse::<usize>().unwrap_or_else(|e| panic!("{}", e)) - 1).collect::<Vec<_>>()
    };
    ($it:ident; [$t:ty]) => {
        $it.map(|s| s.parse::<$t>().unwrap_or_else(|e| panic!("{}", e))).collect::<Vec<_>>()
    };
    ($it:ident; $t:ty) => {
        $it.next().unwrap_or_else(|| panic!("input mismatch")).parse::<$t>().unwrap_or_else(|e| panic!("{}", e))
    };
    ($it:ident; $($t:tt),+) => {
        ($(_read!($it; $t)),*)
    };
}


pub fn main() {
    let _ = ::std::thread::Builder::new().name("run".to_string()).stack_size(32 * 1024 * 1024).spawn(run).unwrap().join();
}

const MOD: usize = 998244353;
// const MOD: usize = 1_000_000_007;
const INF: i64 = std::i64::MAX/2;

struct SCC {
    size: usize,
    edge: Vec<Vec<usize>>,
    inv_edge: Vec<Vec<usize>>,
    ids: Vec<usize>,
}

impl SCC {
    pub fn new(n: usize) -> Self {
        SCC {
            size: n,
            edge: vec![vec![];n],
            inv_edge: vec![vec![];n],
            ids: vec![0;n],
        }
    }
    pub fn add_edge(&mut self, s: usize, t: usize) {
        self.edge[s].push(t);
        self.inv_edge[t].push(s);
    }
    fn dfs1(&self, cur: usize, mut seen: &mut [bool], mut back: &mut Vec<usize>) {
        seen[cur] = true;
        for &e in &self.edge[cur] {
            if seen[e] {
                continue;
            }
            self.dfs1(e, &mut seen, &mut back);
        }
        back.push(cur);
    }
    fn dfs2(&self, cur: usize, mut seen: &mut [bool], mut ids: &mut [usize], id: usize) {
        seen[cur] = true;
        ids[cur] = id;
        for &e in &self.inv_edge[cur] {
            if seen[e] {
                continue;
            }
            self.dfs2(e, &mut seen, &mut ids, id);
        }
    }
    pub fn build(&mut self) {
        let mut seen = vec![false;self.size];
        let mut back = vec![];
        for i in 0..self.size {
            if !seen[i]{
                self.dfs1(i,&mut seen, &mut back);
            }
        }
        seen = vec![false;self.size];
        let mut id = 0;
        let mut ids = vec![0;self.size];
        for &i in back.iter().rev() {
            if !seen[i] {
                self.dfs2(i,&mut seen, &mut ids, id);
                id += 1;
            }
        }
        self.ids = ids;
    }
    pub fn get_ids(&self) -> Vec<usize> {
        self.ids.clone()
    }
}

fn solve() {
    let (n,m) = read!(usize,usize);
    let ab = read!(usize,usize;m);
    let mut scc = SCC::new(n);
    for (a,b) in ab {
        scc.add_edge(a,b);
    }
    scc.build();
    let ret = scc.get_ids();
    let num = ret.iter().max().unwrap();
    let mut ans = vec![vec![];num+1];
    for (i,&a) in ret.iter().enumerate() {
        ans[a].push(i);
    }
    println!("{}",num+1);
    for a in &ans {
        print!("{} ", a.len());
        for &a in a {
            print!("{} ",a);
        }
        println!();
    }
}

fn run() {
    solve();
}