Competitive-Programming/Strongly connected components.cp at master · potter1024/Competitive-Programming · GitHub

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//#include <bits/stdc++.h>
#include <iostream>
#include <climits>
#include <vector>
#include <cstdlib>
#include <iomanip>
#include <algorithm>
#include <fstream>
#include <cmath>
#include<math.h>
#include <set>
#include <time.h>
#include <map>
#include <fstream>
#include <cstdio>
#include <vector>
#include <cstring>
#include <string>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>
#include <algorithm>
#include <array>
#include <bitset>
#include <complex>
#include <numeric>
#include <unordered_map>
using namespace std;
#define sz(a) int((a).size())
#define ll long long
#define pb push_back
#define ld long double
#define mp make_pair
#define vi vector<ll>
#define endl "\n"
#define all(c) (c).begin(),(c).end()
#define allr(c) (c).rbegin(),(c).rend()
#define rep(i,n) for(ll i=0;i<n;i++)
#define cpresent(c,x) (find(all(c),x) != (c).end())
#define input(a,n) for(long long i=0;i<n;i++)cin>>a[i]
#define output(a,n) for(long long i=0;i<n;i++)cout<<a[i]<<" "
#define     she_taught_me_to_code cin.tie(0);cout.tie(0);ios_base::sync_with_stdio(false);cin.tie(NULL);
#define ep 1e-10
#define pi pair<ll,ll>
#define inf 10e9
#define N 1000000
bool sortbysec(const pair<int,int> &a,const pair<int,int> &b)
{
    return (a.second < b.second);
}
ll gcd(ll a,ll b)
{
    if (b == 0)
        return a;
    return gcd(b, a % b);
}
ll lcm1(ll a,ll b)
{
    return (a*b)/gcd(a,b);
}
ll min(ll a,ll b)
{
    if(a<b)
        return a;
    return b;
}
ll max(ll a,ll b)
{
    if(a>b)
        return a;
    return b;}
stack<ll> s;
#define N 1000000
vector<ll> adj[N];
vector<bool> visited(N,0);
vector<ll> scc[N];
void DFSUtil(ll u)
{
    visited[u] = true;
    for (ll i=0; i<adj[u].size(); i++)
    {
        if (visited[adj[u][i]] == false)
        {
            DFSUtil(adj[u][i]);
        }
    }
    s.push(u);
}
void _DFSUtil(ll u,ll index)
{
    visited[u] = true;
    for (ll i=0; i<adj[u].size(); i++)
    {
        if (visited[adj[u][i]] == false)
        {
            _DFSUtil(adj[u][i],index);
        }
    }
    scc[index].pb(u);
}
void DFS(ll n)
{
    for (ll u=1; u<=n; u++)
    {
        if (visited[u] == false)
        {
            DFSUtil(u);
        }
    }
}
void aE(ll u, ll v)
{
    adj[u].push_back(v);
}
int main()
{
    she_taught_me_to_code

    // freopen("input.txt","r",stdin);
    // freopen("output.txt","w",stdout);

    ll n,m;
    cin>>n>>m;
    vector<pair<ll,ll> > r_edges;           // for reverse edges
    for(ll i=0;i<m;i++)
    {
        ll a,b;
        cin>>a>>b;
        aE(a,b);
        r_edges.pb(mp(b,a));
    }
    DFS(n);
    for(ll i=1;i<=n;i++)
        adj[i].erase(all(adj[i]));
    for(ll i=0;i<m;i++)
        aE(r_edges[i].first,r_edges[i].second);
    for(ll i=1;i<=n;i++)
        visited[i]=0;
    ll index=0;
    while(s.empty()==0)
    {
        ll x=s.top();
        s.pop();
        if(visited[x]==1)
            continue;
        _DFSUtil(x,index);
        index++;
    }
    cout<<index<<endl;                          // total number of scc
    for(ll i=0;i<index;i++)
    {
        for(ll j=0;j<scc[i].size();j++)
            cout<<scc[i][j]<<" ";
        cout<<endl;
    }
}