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C.cpp
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C.cpp
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#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
vector<vector<int>> adj;
vector<pair<int, int>> ans;
int node, flag;
void dfs(int u, int p)
{
bool ok = 0;
if (u != node && (int)adj[u].size() - 1 > 1) {
flag = 1;
return;
}
for (auto &v : adj[u]) {
if (v == p) continue;
ok = 1;
dfs(v, u);
}
if (!ok) {
ans.push_back({node, u});
}
}
void solve()
{
int n;
cin >> n;
adj.resize(n + 1);
vector<int> deg(n + 1, 0);
for (int i = 0; i < n - 1; i++) {
int u, v;
cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
deg[u]++, deg[v]++;
}
int d = 0;
for (int i = 1; i <= n; i++) {
if (deg[i] > d) {
node = i;
d = deg[i];
}
}
flag = 0;
dfs(node, -1);
if (flag) cout << "No\n";
else {
cout << "Yes\n";
cout << (int)ans.size() << '\n';
for (int i = 0; i < (int)ans.size(); i++) {
cout << ans[i].first << ' ' << ans[i].second << '\n';
}
}
}
int main()
{
#ifndef ONLINE_JUDGE
//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);
//freopen("Error.txt", "w", stderr);
#endif
ios_base::sync_with_stdio(false);
cin.tie(NULL), cout.tie(NULL);
int t = 1;
//cin >> t;
while (t--) solve();
return 0;
}