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c_cpp
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#include <bits/stdc++.h> using namespace std; typedef long long int ll; #define endl "\n" #define int long long const double PI = 3.14159265358979; const ll INF = 1e18; const ll MOD = 1e9 + 7; const ll nax = 100002; const int LOG = 25; class Solver { int n; vector<vector<int> > adj; vector<int> depth; vector<int> parent; void dfs(int u, int par, int dep) { parent[u] = par; depth[u] = dep; for (int v: adj[u]) { if (v != par) { dfs(v, u, dep + 1); } } } public: void solve() { cin >> n; adj.resize(n + 1); parent.resize(n + 1); depth.resize(n + 1); for (int i = 1; i < n; i++) { int x, y; cin >> x >> y; adj[x].push_back(y); adj[y].push_back(x); } dfs(1, 0, 0); int d1 = 0, n1 = 1; for (int i = 1; i <= n; i++) { if (d1 < depth[i]) { d1 = depth[i]; n1 = i; } } dfs(n1, 0, 0); d1 = 0, n1 = 1; for (int i = 1; i <= n; i++) { if (d1 < depth[i]) { d1 = depth[i]; n1 = i; } } if (d1 & 1) { cout << "-1" << endl; return; } int x = d1 / 2; while(x--) { n1 = parent[n1]; } cout << n1 << endl; } }; signed main() { ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr); int t = 1; // cin >> t; while(t--) { Solver solver; solver.solve(); } return 0; }
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