func_code_string: #include <bits/stdc++.h>   using namespace std;   vector<pair<int, int> > ans;   vector<int> e[100010];   void dfs(int x, int p, int entry) {     ans.emplace_back(x, entry);     if (x == 1) {       for (int it : e[x])         if (it != p) dfs(it, x, ++entry), ans.emplace_back(1, entry);     } else {       int cur = entry;       int sz = e[x].size() - 1;       if (entry - 1 >= sz) {         cur = entry - 1 - sz;         ans.emplace_back(x, cur);         for (int it : e[x])           if (it != p) {             cur++;             dfs(it, x, cur), ans.emplace_back(x, cur);           }       } else {         for (int it : e[x])           if (it != p) {             ++cur;             dfs(it, x, cur), ans.emplace_back(x, cur);             if (cur == sz + 1) {               cur = 0;               ans.emplace_back(x, 0);             }           }       }     }   }   int main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     int n;     cin >> n;     for (int i = 1, u, v; i < n; i++) {       cin >> u >> v;       e[u].emplace_back(v);       e[v].emplace_back(u);     }     dfs(1, 0, 0);     cout << ans.size() <<   n ;     for (auto &[u, v] : ans) cout << u <<     << v <<   n ;   }   