SCC.cpp

/* Strongly Connected Components */
/* Author : M. A. Rafsan Mazumder */

#include <bits/stdc++.h>

using namespace std;

#define MAX 10005
vector<int> adj[MAX];
vector<int> revAdj[MAX];
bool vis[MAX];
stack<int> S;

void stackEmpty()
{
    while(!S.empty()){
        S.pop();
    }
}

void dfs(int u)
{
    vis[u] = true;
    for(int i=0; i<adj[u].size(); i++){
        int v = adj[u][i];
        if(!vis[v]) dfs(v);
    }
    S.push(u);
}

void dfs2(int u)
{
    vis[u] = true;
    for(int i=0; i<revAdj[u].size(); i++){
        int v = revAdj[u][i];
        if(!vis[v]) dfs2(v);
    }
}

int main()
{
    stackEmpty();
    int n, m;
    scanf("%d %d", &n, &m);
    for(int i=1; i<=m; i++){
        int u, v;
        scanf("%d %d", &u, &v);
        adj[u].push_back(v);
        revAdj[v].push_back(u);
    }
    memset(vis, false, sizeof vis);
    for(int i=1; i<=n; i++){
        if(!vis[i]) dfs(i);
    }
    memset(vis, false, sizeof vis);
    int cnt = 0;
    while(!S.empty()){
        int t = S.top();
        S.pop();
        if(!vis[t]){
            cnt++;
            dfs2(t);
        }
    }
    printf("%d", cnt);
}