622E - Ants in Leaves - CodeForces Solution

#include <bits/stdc++.h>

using namespace std;
using ll = long long;

int main(){
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);

    int N, A, B, C, ans=0;
    cin >> N;
    vector<vector<int>> E(N), D(N);

    for (int i=0; i<N-1; i++){
        cin >> A >> B;
        A--; B--;
        E[A].push_back(B);
        E[B].push_back(A);
    }

    auto dfs=[&](auto self, int from, int p, int d)->void{
        if (p == 0) C=from;
        if (p != -1 && E[from].size() == 1) D[C].push_back(d);
        for (auto to : E[from]){
            if (to == p) continue;
            self(self, to, from, d+1);
        }
    };

    dfs(dfs, 0, -1, 0);
    for (int i=0; i<N; i++){
        if (!D[i].empty()){
            int s=0;
            sort(D[i].begin(), D[i].end());
            for (auto x : D[i]) s=max(s+1, x);
            ans = max(ans, s);
        }
    }

    cout << ans << endl;

    return 0;
}