retele.cpp

/***************************************************
 * Alex Palcuie
 * Romania - 2013
 * alex [dot] palcuie [at] gmail [dot] com
 * http://palcu.blogspot.com/
****************************************************/

#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <queue>
#include <bitset>
#include <algorithm>
#include <utility>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <iterator>
#include <cstring>
#include <climits>

using namespace std;

// Defines
#define NAME(n) #n
#define pr(x) db((x), (#x))
#define prv(v,n) dbv((v), (#v), (n))
#define prw(v) dbw((v), (#v))
#define F first
#define S second
#define pb push_back
#define sz size()
#define mp make_pair
typedef unsigned long long ull;
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;

// Helpers
template <typename T> inline void db(const T x, const char * name){
    cerr << name << " = " << x << '\n';
}
template <typename T> inline void dbv(const T * v, const char * name, int n){
    fprintf(stderr, "=== %s ===\n", name);
    for(int i=0; i<n; i++)
        cerr << v[i] << " ";
    cerr << '\n';
}
template <typename T> inline void dbs(T x){
    cerr << x << ' ';
}
template<typename T> void dbw(const std::vector<T>& t, const char * name){
    fprintf(stderr, "=== %s ===\n", name);
    unsigned n = t.size();
    for(typename std::vector<T>::size_type i=0; i<n; ++i)
        std::cerr << t[i] << ' ';
    cerr << '\n';
}

// Structs

// Constants
const int N = 50008;
const int INF = 0x3f3f3f3f;

// Globals
int n, nMuchii;
vector<int> g[N], gReverse[N];
bool isVisited[N];
int order[N], nOrder;
vector<vector<int> > sol;

// Functions
void dfs_rev(int k){
    isVisited[k] = 1;
    for(int i=0; i<gReverse[k].sz; i++){
        int y = gReverse[k][i];
        if(!isVisited[y])
            dfs_rev(y);
    }
    order[nOrder++] = k;
}

void dfs(int k){
    isVisited[k] = 1;
    sol.back().pb(k);
    for(int i=0; i<g[k].sz; i++){
        int y = g[k][i];
        if(!isVisited[y])
            dfs(y);
    }
}

bool comp(vi a, vi b){
    return a[0] > b[0];
}

int main(){
    #ifndef ONLINE_JUDGE
    freopen("retele.in","r",stdin);
    freopen("retele.out","w",stdout);
    #endif

    int i, j;

    cin >> n >> nMuchii;
    for(i=0; i<nMuchii; i++){
        int a, b;
        cin >> a >> b;
        g[a].pb(b);
        gReverse[b].pb(a);
    }

    for(i=1; i<=n; i++)
        if(!isVisited[i])
            dfs_rev(i);

    memset(isVisited, 0, sizeof(isVisited));
    for(i=n-1; i>=0; i--){
        int k = order[i];
        if(!isVisited[k]){
            sol.pb(vector<int>());
            dfs(k);
        }
    }

    cout << sol.sz << '\n';
    for(i=0; i<sol.sz; i++)
        sort(sol[i].begin(), sol[i].end());
    sort(sol.begin(), sol.end());
    for(i=0; i<sol.sz; i++){
        cout << sol[i].sz << ' ';
        for(j=0; j<sol[i].sz; j++)
            cout << sol[i][j] << ' ';
        cout << '\n';
    }

    return 0;
}