并查集找环

传送门

#include <bits/stdc++.h>
using namespace std;
const int N = 1e3 + 10;
int n, m, p[N];
int findd(int x)
{
    while(x != p[x]) x = p[x] = p[p[x]];
    return x;
}
signed main()
{
    ios::sync_with_stdio(false), cin.tie(0);
    cin >> n >> m;
    for(int i = 1; i <= n; ++i) p[i] = i;
    int x, y, ok1 = 0;
    for(int i = 1; i <= m; ++i)
    {
        cin >> x >> y;
        int fx = findd(x), fy = findd(y);
        if(fx == fy) ok1++;
        else p[fy] = fx;
    }
    int ok2 = 0;
    for(int i = 1; i <= n; ++i) if(findd(i) == i) ok2++;
    if(ok1 == 1 && ok2 == 1) cout << "FHTAGN!\n";
    else cout << "NO\n";
    return 0;
}