如果你只过了前五个点，WA 45pts，检查你的 dfs 有没有写挂。

#include <bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n'
const int N = 1e3 + 5;
template<class Tp>
class Ufs {
	private:
		map<Tp, Tp> f;
		Tp root(Tp a) {
			if(f[a] == a) return a;
			f[a] = root(f[a]);
			return f[a];
		}
		Tp a[N];
	public:
		map<Tp, int> s;
		void init(Tp *b, Tp *e) {
			int z = 0;
			for(Tp *i = b; i < e; i++) f[*i] = *i, s[*i] = 1;
		}
		void init(int n) {
			for(Tp i = 1; i <= n; i++) a[i] = i;
			init(a + 1, a + n + 1);
		}
		bool same(Tp a, Tp b) {
			Tp p = root(a), q = root(b);
			return p == q;
		}
		void merge(Tp a, Tp b) {
			Tp p = root(a), q = root(b);
			if(p == q) return;
			if(s[p] > s[q]) swap(p, q);
			f[p] = q;
			s[q] += s[p];
		}
}; Ufs<int> g;
int n, m, x[N], y[N]; set<char> c; vector<char> d;
vector<pair<int, int>> s;
int randint(int l, int r) {
	return rand() % (r - l + 1) + l;
}
void work(char a, char b) {
	int l = randint(0, 3);
	cout<<a; while(l--) cout<<char(randint(0, 25) + 'a'); cout<<b<<endl;
}
void solve() {
	// cout<<"solve"<<endl;
	n = 0, m = randint(1, 5); 
	c.clear(), s.clear(), d.clear();
	while(c.size() < m) c.insert(randint(0, 25) + 'a');
	for(char i : c) d.push_back(i); // cout<<i; cout<<endl;
	int t = randint(0, 1);
	// cout<<"qwq "<<n<<" "<<m<<" "<<t<<endl;
	if(t || m == 1) {
		for(int i = 1; i <= m; i++) x[i] = y[i] = randint(1, 3), n += x[i] + y[i];
	} else {
		int f = randint(1, m), e = randint(1, m);
		while(e == f) e = randint(1, m);
		for(int i = 1; i <= m; i++) {
			if(i == f) x[i] = (y[i] = randint(1, 3) + 1);
			else if(i == e) x[i] = (y[i] = randint(1, 3) - 1);
			else x[i] = y[i] = randint(1, 3);
		 	n += x[i] + y[i];
		}
	}
	for(int i = 1; i <= n / 2; i++) {
		int u = randint(1, m), v = randint(1, m);
		while(!x[u] || !y[v]) u = randint(1, m), v = randint(1, m);
		x[u]--, y[v]--, s.push_back({u, v});
	}
	// cout<<"qwq"<<endl;
	g.init(m);
	for(auto [u, v] : s) g.merge(u, v);
	int b = 1;
	for(int i = 1; i <= m; i++) if(g.s[i] == m) b = 0;
	if(b) {
		// cout<<"qwq"<<endl;
		solve();
		return;
	}
	cout<<n / 2<<endl;
	for(auto [u, v] : s) {
		// cout<<u<<" "<<v<<endl;
		work(d[u - 1], d[v - 1]);
	}
}
signed main() {
	srand(time(0));
	solve();
}