func_code_string: #include <bits/stdc++.h>   #pragma comment(linker,  /STACK:1000000000 )   #pragma GCC optimize( Ofast,no-stack-protector )   using namespace std;   const int maxn = (int)1e5 + 10;   vector<int> ed[maxn];   int sz[maxn];   void dfs(int v, int p) {     sz[v] = 1;     for (int u : ed[v]) {       if (u != p) {         dfs(u, v);         sz[v] += sz[u];       }     }   }   int h[maxn];   vector<pair<pair<int, int>, int> > g[maxn];   long long sum = 0;   set<int> vert[maxn];   int tt = -1;   int tin[maxn], tout[maxn];   void build(int v, int p, int pr, int hh) {     tt++;     tin[v] = tt;     vert[pr].insert(v);     sum += hh;     h[v] = hh;     sz[v] = 1;     vector<int> a;     for (int u : ed[v]) {       if (u == p) {         continue;       }       build(u, v, pr, hh + 1);       sz[v] += sz[u];       if (sz[u] & 1) {         a.push_back(u);       }     }     while ((int)a.size() >= 2) {       int x = a.back();       a.pop_back();       int y = a.back();       a.pop_back();       g[pr].push_back(make_pair(make_pair(x, y), hh));     }     if (!a.empty()) {       g[pr].push_back(make_pair(make_pair(a.back(), v), hh));     }     tout[v] = tt;   }   bool is_anc(int x, int y) { return tin[x] <= tin[y] && tout[y] <= tout[x]; }   int main() {     int n;     long long k;     cin >> n >> k;     for (int i = 0; i < n - 1; i++) {       int x, y;       scanf( %d %d , &x, &y);       x--;       y--;       ed[x].push_back(y);       ed[y].push_back(x);     }     dfs(0, -1);     int v = 0;     while (true) {       bool ok = true;       for (int u : ed[v]) {         if (sz[u] < sz[v] && 2 * sz[u] > n) {           v = u;           ok = false;           break;         }       }       if (ok) {         break;       }     }     for (int u : ed[v]) {       build(u, v, u, 1);       reverse((g[u]).begin(), (g[u]).end());     }     if (k > sum) {       cout <<  NO n  <<   n ;       return 0;     }     set<pair<int, int> > s;     for (int u : ed[v]) {       s.insert(make_pair(sz[u], u));     }     vector<pair<int, int> > res;     if ((k - sum) & 1) {       cout <<  NO n  <<   n ;       return 0;     }     while (!s.empty() && sum != k) {       int u = s.rbegin()->second;       s.erase(*s.rbegin());       if (sz[u] == 1) {         cout <<  NO n  <<   n ;         return 0;       }       if (sum - 2 * g[u].back().second >= k) {         sum -= 2 * g[u].back().second;         sz[u] -= 2;         s.insert(make_pair(sz[u], u));         res.push_back(g[u].back().first);         vert[u].erase(g[u].back().first.first);         vert[u].erase(g[u].back().first.second);         g[u].pop_back();         continue;       }       int x = g[u].back().first.first;       int y = -1;       for (int z : vert[u]) {         if (sum - 2 * h[z] == k && is_anc(z, x)) {           y = z;           break;         }       }       assert(y != -1);       res.push_back(make_pair(x, y));       vert[u].erase(x);       vert[u].erase(y);       break;     }     cout <<  YES n ;     s.clear();     for (int u : ed[v]) {       if (vert[u].size()) {         s.insert(make_pair(vert[u].size(), u));       }     }     while ((int)s.size() > 1) {       int x = s.rbegin()->second;       s.erase(*s.rbegin());       int y = s.rbegin()->second;       s.erase(*s.rbegin());       int a = *vert[x].begin();       vert[x].erase(a);       int b = *vert[y].begin();       vert[y].erase(b);       res.push_back(make_pair(a, b));       if (vert[x].size()) {         s.insert(make_pair(vert[x].size(), x));       }       if (vert[y].size()) {         s.insert(make_pair(vert[y].size(), y));       }     }     int x = s.begin()->second;     assert((int)vert[x].size() == 1);     res.push_back(make_pair(v, *vert[x].begin()));     for (pair<int, int> f : res) {       printf( %d %d n , f.first + 1, f.second + 1);     }   }   