SDA - 2020 2021 - test5 - task 2

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <unordered_map>
#include <unordered_set>

using namespace std;

unordered_map<int, unordered_set<int>> graph;
bool visited[100000] {false};

int dfs(int a, int count = 0){
    visited[a] = true;
    count++;
    for(auto i : graph[a]){
        if(!visited[i])
            count = dfs(i, count);
    }
    return count;
}

int main() {
    int n, m , a, b;
    cin >> n >> m;

    for(int i = 0; i < m; i++){
        cin >> a >> b;
        graph[a].insert(b);
        graph[b].insert(a);
    }
    int res = 0;
    for(int i = 0; i < n; i++){
        if(!visited[i] && dfs(i) > 1)
            res++;
    }
    cout << res;

    return 0;
}