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 (Python):
from collections import deque
class csr:
    def __init__(self,N,edges):
        self.start = [0]*(N+1)
        self.elist = [0]*len(edges)
        for e in edges:
            self.start[e[0]+1] += 1
        for i in range(1,N+1):
            self.start[i] += self.start[i-1] 
        counter = self.start[:]
        for e in edges:
            self.elist[counter[e[0]]] = e[1]
            counter[e[0]] += 1

class scc_graph:
    def __init__(self,N):
        self.N = N
        self.edges = []
    
    def add_edge(self,v,w):
        self.edges.append((v,w))

    def scc_ids(self):
        g = csr(self.N,self.edges)
        now_ord = group_num = 0
        visited = deque()
        low = [0]*self.N
        order = [-1]*self.N
        ids = [0]*self.N
        parent = [-1]*self.N
        for i in range(self.N):
            if order[i] == -1:
                stack = []
                stack.append(i)
                stack.append(i)
                while stack:
                    v = stack.pop()
                    if order[v] == -1:
                        low[v] = order[v] = now_ord
                        now_ord += 1
                        visited.append(v)
                        for i in range(g.start[v],g.start[v+1]):
                            to = g.elist[i]
                            if order[to] == -1:
                                stack.append(to)
                                stack.append(to)
                                parent[to] = v
                            else:
                                low[v] = min(low[v],order[to])
                    else:
                        if low[v] == order[v]:
                            while True:
                                u = visited.pop()
                                order[u] = self.N
                                ids[u] = group_num
                                if u == v:
                                    break
                            group_num += 1
                        if parent[v] != -1:
                            low[parent[v]] = min(low[parent[v]],low[v])
        for i,x in enumerate(ids):
            ids[i] = group_num-1-x

        return group_num,ids
    
    def scc(self):
        group_num,ids = self.scc_ids()
        groups = [[] for _ in range(group_num)]
        for i,x in enumerate(ids):
            groups[x].append(i)
        return groups
    
import sys
readline = sys.stdin.buffer.readline
read = sys.stdin.buffer.read
N,M = map(int,readline().split())
ab = list(map(int,read().split()))
sg = scc_graph(N)

it = iter(ab)
for a,b in zip(it,it):
    sg.add_edge(a,b)

scc = sg.scc()
print(len(scc))
for group in scc:
    print(str(len(group))+' '+' '.join(map(str,group)))

Solution (Python):
from collections import deque
class csr:
    def __init__(self,N,edges):
        self.start = [0]*(N+1)
        self.elist = [0]*len(edges)
        for e in edges:
            self.start[e[0]+1] += 1
        for i in range(1,N+1):
            self.start[i] += self.start[i-1] 
        counter = self.start[:]
        for e in edges:
            self.elist[counter[e[0]]] = e[1]
            counter[e[0]] += 1

class scc_graph:
    def __init__(self,N):
        self.N = N
        self.edges = []
    
    def add_edge(self,v,w):
        self.edges.append((v,w))

    def scc_ids(self):
        g = csr(self.N,self.edges)
        now_ord = group_num = 0
        visited = deque()
        low = [0]*self.N
        order = [-1]*self.N
        ids = [0]*self.N
        parent = [-1]*self.N
        for i in range(self.N):
            if order[i] == -1:
                stack = deque()
                stack.append(i)
                stack.append(i)
                while stack:
                    v = stack.pop()
                    if order[v] == -1:
                        low[v] = order[v] = now_ord
                        now_ord += 1
                        visited.append(v)
                        for i in range(g.start[v],g.start[v+1]):
                            to = g.elist[i]
                            if order[to] == -1:
                                stack.append(to)
                                stack.append(to)
                                parent[to] = v
                            else:
                                low[v] = min(low[v],order[to])
                    else:
                        if low[v] == order[v]:
                            while True:
                                u = visited.pop()
                                order[u] = self.N
                                ids[u] = group_num
                                if u == v:
                                    break
                            group_num += 1
                        if parent[v] != -1:
                            low[parent[v]] = min(low[parent[v]],low[v])
        for i,x in enumerate(ids):
            ids[i] = group_num-1-x

        return group_num,ids
    
    def scc(self):
        group_num,ids = self.scc_ids()
        groups = [[] for _ in range(group_num)]
        for i,x in enumerate(ids):
            groups[x].append(i)
        return groups
    
import sys
readline = sys.stdin.buffer.readline
read = sys.stdin.buffer.read
N,M = map(int,readline().split())
ab = list(map(int,read().split()))
sg = scc_graph(N)

it = iter(ab)
for a,b in zip(it,it):
    sg.add_edge(a,b)

scc = sg.scc()
print(len(scc))
for group in scc:
    print(*([len(group)] + group))

Solution (Python):
from collections import deque
class csr:
    def __init__(self,N,edges):
        self.start = [0]*(N+1)
        self.elist = [0]*len(edges)
        for e in edges:
            self.start[e[0]+1] += 1
        for i in range(1,N+1):
            self.start[i] += self.start[i-1] 
        counter = self.start[:]
        for e in edges:
            self.elist[counter[e[0]]] = e[1]
            counter[e[0]] += 1

class scc_graph:
    def __init__(self,N):
        self.N = N
        self.edges = []
    
    def add_edge(self,v,w):
        self.edges.append((v,w))

    def scc_ids(self):
        g = csr(self.N,self.edges)
        now_ord = group_num = 0
        visited = deque()
        low = [0]*self.N
        order = [-1]*self.N
        ids = [0]*self.N
        parent = [-1]*self.N
        for i in range(self.N):
            if order[i] == -1:
                stack = deque()
                stack.append(i)
                stack.append(i)
                while stack:
                    v = stack.pop()
                    if order[v] == -1:
                        low[v] = order[v] = now_ord
                        now_ord += 1
                        visited.append(v)
                        for i in range(g.start[v],g.start[v+1]):
                            to = g.elist[i]
                            if order[to] == -1:
                                stack.append(to)
                                stack.append(to)
                                parent[to] = v
                            else:
                                low[v] = min(low[v],order[to])
                    else:
                        if low[v] == order[v]:
                            while True:
                                u = visited.pop()
                                order[u] = self.N
                                ids[u] = group_num
                                if u == v:
                                    break
                            group_num += 1
                        if parent[v] != -1:
                            low[parent[v]] = min(low[parent[v]],low[v])
        for i,x in enumerate(ids):
            ids[i] = group_num-1-x

        return group_num,ids
    
    def scc(self):
        group_num,ids = self.scc_ids()
        groups = [[] for _ in range(group_num)]
        for i,x in enumerate(ids):
            groups[x].append(i)
        return groups
    
import sys
readline = sys.stdin.buffer.readline
read = sys.stdin.buffer.read
N,M = map(int,readline().split())
ab = list(map(int,read().split()))
sg = scc_graph(N)

it = iter(ab)
for a,b in zip(it,it):
    sg.add_edge(a,b)

scc = sg.scc()
print(len(scc))
for group in scc:
    print(str(len(group))+' '+' '.join(map(str,group)))

Solution (Python):
from collections import deque
class csr:
    def __init__(self,N,edges):
        self.start = [0]*(N+1)
        self.elist = [0]*len(edges)
        for e in edges:
            self.start[e[0]+1] += 1
        for i in range(1,N+1):
            self.start[i] += self.start[i-1] 
        counter = self.start[:]
        for e in edges:
            self.elist[counter[e[0]]] = e[1]
            counter[e[0]] += 1

class scc_graph:
    def __init__(self,N):
        self.N = N
        self.edges = []
    
    def add_edge(self,v,w):
        self.edges.append((v,w))

    def scc_ids(self):
        g = csr(self.N,self.edges)
        now_ord = group_num = 0
        visited = deque()
        low = [0]*self.N
        order = [-1]*self.N
        ids = [0]*self.N
        parent = [-1]*self.N
        for i in range(self.N):
            if order[i] == -1:
                stack = deque()
                stack.append(i)
                stack.append(i)
                while stack:
                    v = stack.pop()
                    if order[v] == -1:
                        low[v] = order[v] = now_ord
                        now_ord += 1
                        visited.append(v)
                        for i in range(g.start[v],g.start[v+1]):
                            to = g.elist[i]
                            if order[to] == -1:
                                stack.append(to)
                                stack.append(to)
                                parent[to] = v
                            else:
                                low[v] = min(low[v],order[to])
                    else:
                        if low[v] == order[v]:
                            while True:
                                u = visited.pop()
                                order[u] = self.N
                                ids[u] = group_num
                                if u == v:
                                    break
                            group_num += 1
                        if parent[v] != -1:
                            low[parent[v]] = min(low[parent[v]],low[v])
        for i,x in enumerate(ids):
            ids[i] = group_num-1-x

        return group_num,ids
    
    def scc(self):
        group_num,ids = self.scc_ids()
        groups = [[] for _ in range(group_num)]
        for i,x in enumerate(ids):
            groups[x].append(i)
        return groups
    
import sys
input = sys.stdin.buffer.readline
N,M = map(int,input().split())
sg = scc_graph(N)
for i in range(M):
    a,b = map(int,input().split())
    sg.add_edge(a,b)

scc = sg.scc()
print(len(scc))
for group in scc:
    print(str(len(group))+' '+' '.join(map(str,group)))

Solution (Python):
import sys
range = xrange
input = raw_input
 
def find_SCC(coupl):
    SCC, S, P = [], [], []
    depth = [0] * len(coupl)
 
    stack = list(range(len(coupl)))
    while stack:
        node = stack.pop()
        if node < 0:
            d = depth[~node] - 1
            if P[-1] > d:
                SCC.append(S[d:])
                del S[d:], P[-1]
                for node in SCC[-1]:
                    depth[node] = -1
        elif depth[node] > 0:
            while P[-1] > depth[node]:
                P.pop()
        elif depth[node] == 0:
            S.append(node)
            P.append(len(S))
            depth[node] = len(S)
            stack.append(~node)
            stack += coupl[node]
    return SCC[::-1]
 
inp = [int(x) for x in sys.stdin.read().split()]; ii = 0
 
n = inp[ii]; ii += 1
m = inp[ii]; ii += 1
 
coupl = [[] for _ in range(n)]
for _ in range(m):
    u = inp[ii]; ii += 1
    v = inp[ii]; ii += 1
    coupl[u].append(v)
 
SCC = find_SCC(coupl)
out = [len(SCC)]
for scc in SCC:
    out.append(len(scc))
    for node in scc:
        out.append(node)
print ' '.join(str(x) for x in out)

Solution (Python):



code_scc_graph = r"""




// 元のライブラリの private を剥がした

// >>> AtCoder >>>













namespace atcoder {
namespace internal {

template <class E> struct csr {
    std::vector<int> start;
    std::vector<E> elist;
    csr(int n, const std::vector<std::pair<int, E>>& edges)
        : start(n + 1), elist(edges.size()) {
        for (auto e : edges) {
            start[e.first + 1]++;
        }
        for (int i = 1; i <= n; i++) {
            start[i] += start[i - 1];
        }
        auto counter = start;
        for (auto e : edges) {
            elist[counter[e.first]++] = e.second;
        }
    }
};

// Reference:
// R. Tarjan,
// Depth-First Search and Linear Graph Algorithms
struct scc_graph {
  public:
    scc_graph(int n) : _n(n) {}

    int num_vertices() { return _n; }

    void add_edge(int from, int to) { edges.push_back({from, {to}}); }

    // @return pair of (
    std::pair<int, std::vector<int>> scc_ids() {
        auto g = csr<edge>(_n, edges);
        int now_ord = 0, group_num = 0;
        std::vector<int> visited, low(_n), ord(_n, -1), ids(_n);
        visited.reserve(_n);
        auto dfs = [&](auto self, int v) -> void {
            low[v] = ord[v] = now_ord++;
            visited.push_back(v);
            for (int i = g.start[v]; i < g.start[v + 1]; i++) {
                auto to = g.elist[i].to;
                if (ord[to] == -1) {
                    self(self, to);
                    low[v] = std::min(low[v], low[to]);
                } else {
                    low[v] = std::min(low[v], ord[to]);
                }
            }
            if (low[v] == ord[v]) {
                while (true) {
                    int u = visited.back();
                    visited.pop_back();
                    ord[u] = _n;
                    ids[u] = group_num;
                    if (u == v) break;
                }
                group_num++;
            }
        };
        for (int i = 0; i < _n; i++) {
            if (ord[i] == -1) dfs(dfs, i);
        }
        for (auto& x : ids) {
            x = group_num - 1 - x;
        }
        return {group_num, ids};
    }

    std::vector<std::vector<int>> scc() {
        auto ids = scc_ids();
        int group_num = ids.first;
        std::vector<int> counts(group_num);
        for (auto x : ids.second) counts[x]++;
        std::vector<std::vector<int>> groups(ids.first);
        for (int i = 0; i < group_num; i++) {
            groups[i].reserve(counts[i]);
        }
        for (int i = 0; i < _n; i++) {
            groups[ids.second[i]].push_back(i);
        }
        return groups;
    }

  private:
    int _n;
    struct edge {
        int to;
    };
    std::vector<std::pair<int, edge>> edges;
};

}  // namespace internal

}  // namespace atcoder






namespace atcoder {

struct scc_graph {
  public:
    scc_graph() : internal(0) {}
    scc_graph(int n) : internal(n) {}

    void add_edge(int from, int to) {
        int n = internal.num_vertices();
        assert(0 <= from && from < n);
        assert(0 <= to && to < n);
        internal.add_edge(from, to);
    }

    std::vector<std::vector<int>> scc() { return internal.scc(); }

//  private:
    internal::scc_graph internal;
};

}  // namespace atcoder



// <<< AtCoder <<<

using namespace std;
using namespace atcoder;



struct SCCGraph{
    PyObject_HEAD
    scc_graph* graph;
    const int n() const { return graph->internal.num_vertices(); }
};


extern PyTypeObject SCCGraphType;


// >>> SCCGraph definition >>>

static void SCCGraph_dealloc(SCCGraph* self){
    delete self->graph;
    Py_TYPE(self)->tp_free((PyObject*)self);
}
static PyObject* SCCGraph_new(PyTypeObject* type, PyObject* args, PyObject* kwds){
    return type->tp_alloc(type, 0);
}
static int SCCGraph_init(SCCGraph* self, PyObject* args){
    long n;
    if(!PyArg_ParseTuple(args, "l", &n)) return -1;
    if(n < 0 || n > (long)1e8){
        PyErr_Format(PyExc_IndexError,
            "SCCGraph constructor constraint error (constraint: 0<=n<=1e8, got n=%d)", n);
        return -1;
    }
    self->graph = new scc_graph(n);
    return 0;
}
static PyObject* SCCGraph_add_edge(SCCGraph* self, PyObject* args){
    long from, to;
    PARSE_ARGS("ll", &from, &to);
    if(from < 0 || from >= self->n() || to < 0 || to >= self->n()){
        PyErr_Format(PyExc_IndexError,
            "SCCGraph add_ede index out of range (n=%d, from=%d, to=%d)", self->n(), from, to);
        return (PyObject*)NULL;
    }
    self->graph->add_edge(from, to);
    Py_RETURN_NONE;
}
static PyObject* SCCGraph_scc(SCCGraph* self, PyObject* args){
    const vector<vector<int>>& scc = self->graph->scc();
    PyObject* list = PyList_New(scc.size());
    for(int i = 0; i < scc.size(); i++){
        PyObject* lst = PyList_New(scc[i].size());
        for(int j = 0; j < scc[i].size(); j++){
            PyList_SET_ITEM(lst, j, Py_BuildValue("l", scc[i][j]));
        }
        PyList_SET_ITEM(list, i, lst);
    }
    return list;
}
/*
static PyObject* SCCGraph_repr(PyObject* self){
    PyObject* res = PyUnicode_FromFormat("SCCGraph()");
    return res;
}
*/
static PyMethodDef SCCGraph_methods[] = {
    {"add_edge", (PyCFunction)SCCGraph_add_edge, METH_VARARGS, "Add clause"},
    {"scc", (PyCFunction)SCCGraph_scc, METH_VARARGS, "Check if problem satisfiable"},
    {NULL}  /* Sentinel */
};
PyTypeObject SCCGraphType = {
    PyObject_HEAD_INIT(NULL)
    "acl_scc.SCCGraph",                 /*tp_name*/
    sizeof(SCCGraph),                   /*tp_basicsize*/
    0,                                  /*tp_itemsize*/
    (destructor)SCCGraph_dealloc,       /*tp_dealloc*/
    0,                                  /*tp_print*/
    0,                                  /*tp_getattr*/
    0,                                  /*tp_setattr*/
    0,                                  /*reserved*/
    0,//SCCGraph_repr,                    /*tp_repr*/
    0,                                  /*tp_as_number*/
    0,                                  /*tp_as_sequence*/
    0,                                  /*tp_as_mapping*/
    0,                                  /*tp_hash*/
    0,                                  /*tp_call*/
    0,                                  /*tp_str*/
    0,                                  /*tp_getattro*/
    0,                                  /*tp_setattro*/
    0,                                  /*tp_as_buffer*/
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/
    0,                                  /*tp_doc*/
    0,                                  /*tp_traverse*/
    0,                                  /*tp_clear*/
    0,                                  /*tp_richcompare*/
    0,                                  /*tp_weaklistoffset*/
    0,                                  /*tp_iter*/
    0,                                  /*tp_iternext*/
    SCCGraph_methods,                   /*tp_methods*/
    0,                                  /*tp_members*/
    0,                                  /*tp_getset*/
    0,                                  /*tp_base*/
    0,                                  /*tp_dict*/
    0,                                  /*tp_descr_get*/
    0,                                  /*tp_descr_set*/
    0,                                  /*tp_dictoffset*/
    (initproc)SCCGraph_init,            /*tp_init*/
    0,                                  /*tp_alloc*/
    SCCGraph_new,                       /*tp_new*/
    0,                                  /*tp_free*/
    0,                                  /*tp_is_gc*/
    0,                                  /*tp_bases*/
    0,                                  /*tp_mro*/
    0,                                  /*tp_cache*/
    0,                                  /*tp_subclasses*/
    0,                                  /*tp_weaklist*/
    0,                                  /*tp_del*/
    0,                                  /*tp_version_tag*/
    0,                                  /*tp_finalize*/
};

// <<< SCCGraph definition <<<


static PyModuleDef acl_sccmodule = {
    PyModuleDef_HEAD_INIT,
    "acl_scc",
    NULL,
    -1,
};

PyMODINIT_FUNC PyInit_acl_scc(void)
{
    PyObject* m;
    if(PyType_Ready(&SCCGraphType) < 0) return NULL;

    m = PyModule_Create(&acl_sccmodule);
    if(m == NULL) return NULL;

    Py_INCREF(&SCCGraphType);
    if (PyModule_AddObject(m, "SCCGraph", (PyObject*)&SCCGraphType) < 0) {
        Py_DECREF(&SCCGraphType);
        Py_DECREF(m);
        return NULL;
    }
    
    return m;
}
"""
code_scc_graph_setup = r"""
from distutils.core import setup, Extension
module = Extension(
    "acl_scc",
    sources=["scc_graph.cpp"],
    extra_compile_args=["-O3", "-march=native", "-std=c++14"]
)
setup(
    name="acl_scc",
    version="0.0.1",
    description="wrapper for atcoder library scc",
    ext_modules=[module]
)
"""

import os
import sys

if sys.argv[-1] == "ONLINE_JUDGE" or os.getcwd() != "/imojudge/sandbox":
    with open("scc_graph.cpp", "w") as f:
        f.write(code_scc_graph)
    with open("scc_graph_setup.py", "w") as f:
        f.write(code_scc_graph_setup)
    os.system(f"{sys.executable} scc_graph_setup.py build_ext --inplace")

from acl_scc import SCCGraph


def main():
    N, M = map(int, sys.stdin.buffer.readline().split())
    m = map(int, sys.stdin.buffer.read().split())
    g = SCCGraph(N)
    for a, b in zip(m, m):
        g.add_edge(a, b)
    scc = g.scc()
    print(len(scc))
    for v in scc:
        print(len(v), " ".join(map(str, v)))

main()

Solution (Python):
import sys
input = sys.stdin.readline
sys.setrecursionlimit(1000000)

class SCC:

    def __init__(self, n):
        self.n = n
        self.graph = [[] for i in range(n)]
        self.graph_rev = [[] for i in range(n)]
        self.used = [False]*n

    def add_edge(self, fr, to):
        if fr == to:
            return
        self.graph[fr].append(to)
        self.graph_rev[to].append(fr)

    def dfs(self, node, graph):
        self.used[node] = True
        for nex in graph[node]:
            if self.used[nex]:
                continue
            self.dfs(nex,graph)
        self.order.append(node)

    def first_dfs(self):
        self.used = [False]*self.n
        self.order = []
        for i in range(self.n):
            if self.used[i]:
                continue
            self.dfs(i,self.graph)
    
    def second_dfs(self):
        self.used = [False]*self.n
        self.ans = []
        for node in reversed(self.order):
            if self.used[node]:
                continue
            self.used[node] = True
            self.order = []
            self.dfs(node, self.graph_rev)
            
            self.ans.append(self.order)

    def scc(self):
        self.first_dfs()
        self.second_dfs()
        return self.ans
        
def main():
    n,m = map(int,input().split())
    scc = SCC(n)
    for _ in range(m):
        a,b = map(int,input().split())
        scc.add_edge(a,b)

    ans = scc.scc()

    print(len(ans))
    for i in ans:
        print(len(i),*i)

if __name__ == "__main__":
    main()

Solution (Python):
import sys
input = sys.stdin.readline
sys.setrecursionlimit(1000000)

class SCC:

    def __init__(self, n):
        self.n = n
        self.graph = [[] for i in range(n)]
        self.graph_rev = [[] for i in range(n)]
        self.used = [0]*n

    def add_edge(self, fr, to):
        if fr == to:
            return
        self.graph[fr].append(to)
        self.graph_rev[to].append(fr)

    def dfs(self, node, graph):
        self.used[node] = 1
        for nex in graph[node]:
            if self.used[nex]:
                continue
            self.dfs(nex,graph)
        self.order.append(node)

    def first_dfs(self):
        self.used = [0]*self.n
        self.order = []
        for i in range(self.n):
            if self.used[i]:
                continue
            self.dfs(i,self.graph)
    
    def second_dfs(self):
        self.used = [0]*self.n
        self.ans = []
        for node in reversed(self.order):
            if self.used[node]:
                continue
            self.used[node] = 1
            self.order = []
            self.dfs(node, self.graph_rev)
            self.order.reverse()
            self.ans.append(self.order)

    def scc(self):
        self.first_dfs()
        self.second_dfs()
        return self.ans
        
def main():
    n,m = map(int,input().split())
    scc = SCC(n)
    for _ in range(m):
        a,b = map(int,input().split())
        scc.add_edge(a,b)

    ans = scc.scc()

    print(len(ans))
    for i in ans:
        print(len(i),*i)

if __name__ == "__main__":
    main()

Solution (Python):
import sys
input = sys.stdin.readline
sys.setrecursionlimit(1000000)

class SCC:

    def __init__(self, n):
        self.n = n
        self.graph = [[] for i in range(n)]
        self.graph_rev = [[] for i in range(n)]
        self.used = [False]*n

    def add_edge(self, fr, to):
        if fr == to:
            return
        self.graph[fr].append(to)
        self.graph_rev[to].append(fr)

    def dfs(self, node, graph):
        self.used[node] = True
        for nex in graph[node]:
            if self.used[nex]:
                continue
            self.dfs(nex,graph)
        self.order.append(node)

    def first_dfs(self):
        self.used = [False]*self.n
        self.order = []
        for i in range(self.n):
            if self.used[i]:
                continue
            self.dfs(i,self.graph)
    
    def second_dfs(self):
        self.used = [False]*self.n
        self.ans = []
        for node in reversed(self.order):
            if self.used[node]:
                continue
            self.used[node] = True
            self.order = []
            self.dfs(node, self.graph_rev)
            self.order.reverse()
            self.ans.append(self.order)

    def scc(self):
        self.first_dfs()
        self.second_dfs()
        return self.ans
        
def main():
    n,m = map(int,input().split())
    scc = SCC(n)
    for _ in range(m):
        a,b = map(int,input().split())
        scc.add_edge(a,b)

    ans = scc.scc()

    print(len(ans))
    for i in ans:
        print(len(i),*i)

if __name__ == "__main__":
    main()

Solution (Python):
import sys
input = sys.stdin.readline
sys.setrecursionlimit(1000000)

class SCC:

    def __init__(self, n):
        self.n = n
        self.graph = [[] for i in range(n)]
        self.graph_rev = [[] for i in range(n)]
        self.used = [False]*n

    def add_edge(self, fr, to):
        if fr == to:
            return
        self.graph[fr].append(to)
        self.graph_rev[to].append(fr)

    def dfs(self, node, graph):
        self.used[node] = True
        for nex in graph[node]:
            if self.used[nex]:
                continue
            self.dfs(nex,graph)
        self.order.append(node)

    def first_dfs(self):
        self.used = [False]*self.n
        self.order = []
        for i in range(self.n):
            if self.used[i]:
                continue
            self.dfs(i,self.graph)
    
    def second_dfs(self):
        self.used = [False]*self.n
        self.ans = []
        for node in reversed(self.order):
            if self.used[node]:
                continue
            self.used[node] = True
            self.order = []
            self.dfs(node, self.graph_rev)
            self.order.reverse()
            self.ans.append(self.order)

    def scc(self):
        self.first_dfs()
        self.second_dfs()
        return self.ans
        

n,m = map(int,input().split())
scc = SCC(n)
for _ in range(m):
    a,b = map(int,input().split())
    scc.add_edge(a,b)

ans = scc.scc()

print(len(ans))
for i in ans:
    print(len(i),*i)

Solution (Python):
import sys
input = sys.stdin.buffer.readline
sys.setrecursionlimit(10 ** 7)


class StrongConnectedComponents:
    def __init__(self, n):
        self.n = n
        self.G = [[] for _ in range(n)]
        self.rG = [[] for _ in range(n)]
        self.cmp = [-1] * n

    def add_edge(self, frm, to):
        self.G[frm].append(to)
        self.rG[to].append(frm)

    def dfs(self, s):
        self.used[s] = 1
        for t in self.G[s]:
            if not self.used[t]:
                self.dfs(t)
        self.vs.append(s)

    def rdfs(self, s, k):
        self.used[s] = 1
        self.cmp[s] = k
        for t in self.rG[s]:
            if not self.used[t]:
                self.rdfs(t, k)

    def scc(self):
        self.vs = []
        self.used = [0] * self.n
        for v in range(self.n):
            if not self.used[v]:
                self.dfs(v)
        self.used = [0] * self.n
        k = 0
        for v in reversed(self.vs):
            if not self.used[v]:
                self.rdfs(v, k)
                k += 1
        return k, self.make_pair(k)

    def make_pair(self, k):
        res = [[] for _ in range(k)]
        for i, v in enumerate(self.cmp):
            res[v].append(i)
        return res


N, M = map(int, input().split())
g = StrongConnectedComponents(N)
for _ in range(M):
    a, b = map(int, input().split())
    g.add_edge(a, b)
label, group = g.scc()

print(label)
for x in group:
    print(len(x), end=" ")
    print(*x, sep=" ")