justone.cpp

#include <bits/stdc++.h>
using namespace std;

#define int long long
#define vi vector<int>
#define ii pair<int,int>
#define fi first
#define sc second
#define stoi stoll
#define popcnt __builtin_popcount
#define getbit(x, k) ((x >> k) & 1)
#define all(x) (x).begin(),(x).end()
#define FOR(i,j,k) for(int i=j; i<k; i++)
#define look(a) cerr <<#a<<": "<<a<<endl;
#define look2(a,b) cerr <<#a<<": "<<a<<" | "<<#b<<": "<<b<< endl;
const int N = 2e5+5;

bool path[N];
int t,s;
vi a[N];

void dfs(int n){
    path[n] = true;
    t++;
    s += a[n].size();
    FOR(i,0,a[n].size()) if (!path[a[n][i]]) dfs(a[n][i]);
}

void solve()
{
    int n,m;
    cin >> n >> m;
    FOR(i,0,m){
        int x,y;
        cin >> x >> y;
        a[x-1].push_back(y-1);
        a[y-1].push_back(x-1);
    }
    int ans = 1;
    FOR(i,0,n) path[i] = false;
    FOR(i,0,n)
        if (!path[i]){
            t = 0;
            s = 0;
            dfs(i);
            if (s == (t*2)) ans = (ans*2) % 998244353;
            else ans = 0;
        }
    cout << ans;
}

signed main()
{
    cin.tie(0)->sync_with_stdio(0);
    freopen("in", "r", stdin);
    freopen("out", "w", stdout);
    int T = 1;
    // cin >> T;
    while (T--) {
        solve();
        cout << '\n';
    }
    cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
}