duongdi.cpp

#include<iostream>
#include<vector>
#include<cstdlib>

#define long long long

using namespace std;

long n, m, ans = 0;
vector<vector<long>> edg(10);
vector<bool> tic(10, 0);

void dfs(long i, long cnt)
{
    if (cnt == n){
        ++ans;
        return;
    }
    for (const auto &j : edg[i])
        if (!tic[j]){
            tic[j] = 1;
            dfs(j, cnt+1);
            tic[j] = 0;
        }
}

int main()
{
    cin.tie(0)->sync_with_stdio(0);
    cout.tie(0)->sync_with_stdio(0);
    //freopen("duongdi.inp", "r", stdin);
    cin >> n >> m;
    while (m--){
        long x, y;
        cin >> x >> y;
        edg[x].push_back(y);
        edg[y].push_back(x);
    }
    tic[1] = 1;
    dfs(1, 1);
    cout << ans << '\n';
    return 0;
}