Problem: 2063C - Remove Exactly Two
Language: java

Solution 1 (runtime: 905 ms):
import java.io.*;
import java.util.*;

public class RemoveExactlyTwo {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter pw = new PrintWriter(System.out);

        int tc = Integer.parseInt(br.readLine());

        while (tc-- > 0) {
            int N = Integer.parseInt(br.readLine());

            // if (N <)

            ArrayList<Integer>[] adj = new ArrayList[N];
            HashMap<Integer, Integer> degCnt = new HashMap<>();

            for (int i = 0; i < N; i++) {
                adj[i] = new ArrayList<>(); 
            }

            for (int i = 0; i < N-1; i++) {
                String s = br.readLine();
                StringTokenizer st1 = new StringTokenizer(s);

                int a = Integer.parseInt(st1.nextToken()) - 1;
                int b = Integer.parseInt(st1.nextToken()) - 1;

                adj[a].add(b);
                adj[b].add(a);
            }

            for (int i = 0; i < N; i++) {
                int deg = adj[i].size();
                degCnt.put(i, deg);
            }
            int res = 1;
            ArrayList<Integer> maxKeys = getBiggestKeys(degCnt);

            if (maxKeys.size() == 1) {
                res += degCnt.get(maxKeys.get(0)) - 1;
                degCnt.remove(maxKeys.get(0));

                for (int n : adj[maxKeys.get(0)]) {
                    degCnt.put(n, degCnt.get(n)-1);
                }

                res += degCnt.get(getBiggestKeys(degCnt).get(0)) - 1;
            } else {
                int max = degCnt.get(maxKeys.get(0));
                boolean done = false;
                for (int key : maxKeys) {
                    ArrayList<Integer> affected = adj[key];
                    int affectedCount = 0;
                    for (int v : affected) {
                        if (degCnt.get(v) == max) {
                            affectedCount++;
                        }
                    }

                    if (maxKeys.size() - affectedCount > 1) {
                        res = max * 2 - 1;
                        done = true;
                        break;
                    }
                }

                if (!done) {
                    res = max*2-2;
                }
            }

            pw.println(res);
        }

        pw.close();
    }

    static ArrayList<Integer> getBiggestKeys(HashMap<Integer, Integer> hm) {
        ArrayList<Integer> maxKeys = new ArrayList<>();
        for (Map.Entry<Integer, Integer> entry : hm.entrySet()) {
            int key = entry.getKey();
            int val = entry.getValue();

            if (maxKeys.size() == 0 || val >= hm.get(maxKeys.get(0))) {
                if (maxKeys.size() == 0 || val > hm.get(maxKeys.get(0))) {
                    maxKeys.clear();
                    maxKeys.add(key);
                } else {
                    maxKeys.add(key);
                }
            }
        }
        return maxKeys;
    }
}

Solution 2 (runtime: 1093 ms):
  
/* package codechef; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

public class Main {

    //------------------------------------------main--------------------------------------------------//
    public static void main(String[] args) throws java.lang.Exception {
        OutputStream outputStream = System.out;
        PrintWriter out = new PrintWriter(outputStream);
        FastReader sc = new FastReader();
        Task s = new Task(sc, out);
        s.solve();
        out.close();
        // your code goes here"
    }
}

class FastReader {

    BufferedReader br;
    StringTokenizer st;

    public FastReader() {
        br = new BufferedReader(new InputStreamReader(System.in));
    }

    String next() {
        while (st == null || !st.hasMoreElements()) {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return st.nextToken();
    }

    int nextInt() {
        return Integer.parseInt(next());
    }

    long nextLong() {
        return Long.parseLong(next());
    }

    double nextDouble() {
        return Double.parseDouble(next());
    }

    String nextLine() {
        String str = "";
        try {
            str = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return str;
    }

    public int[] readIntArray(int n) throws IOException {
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) {
            arr[i] = nextInt();
        }
        return arr;
    }

    public long[] readLongArray(int n) throws IOException {
        long[] arr = new long[n];
        for (int i = 0; i < n; i++) {
            arr[i] = nextLong();
        }
        return arr;
    }
}

class Task {

    PrintWriter out;
    FastReader sc;

    Task(FastReader sc, PrintWriter out) {
        this.sc = sc;
        this.out = out;
    }
    //----------------------------------------------inputfunction------------------------------------------//

    String st() {
        return sc.nextLine();
    }

    int i() {
        return sc.nextInt();
    }

    long l() {
        return sc.nextLong();
    }

    double d() {
        return sc.nextDouble();
    }

    //---------------------------------------------absolute----------------------------------------------//
    public long abs(long a) {
        return a < 0 ? -a : a;
    }

    public int abs(int a) {
        return a < 0 ? -a : a;
    }

    //-------------------------------------------max--------------------------------------------------//
    public int max(int a, int b) {
        return a >= b ? a : b;
    }

    public long max(long a, long b) {
        return a >= b ? a : b;
    }

    public int max(int a, int b, int c) {
        return Math.max(a, Math.max(b, c));
    }

    public long max(long a, long b, long c) {
        return Math.max(a, Math.max(b, c));
    }

    //------------------------------------------min---------------------------------------------------//
    public int min(int a, int b) {
        return a <= b ? a : b;
    }

    public long min(long a, long b) {
        return a <= b ? a : b;
    }

    public int min(int a, int b, int c) {
        return Math.min(a, Math.min(b, c));
    }

    public long min(long a, long b, long c) {
        return Math.min(a, Math.min(b, c));
    }

    //----------------------------------------sortingfunction---------------------------------------------//
    private void sort(int[] arr) {
        int n = arr.length;
        List<Integer> list = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            list.add(arr[i]);
        }
        Collections.sort(list);
        for (int i = 0; i < n; i++) {
            arr[i] = list.get(i);
        }
    }

    private void sort(char[] arr) {
        int n = arr.length;
        List<Character> list = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            list.add(arr[i]);
        }
        Collections.sort(list);
        for (int i = 0; i < n; i++) {
            arr[i] = list.get(i);
        }
    }

    private void rsort(char[] arr) {
        int n = arr.length;
        List<Character> list = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            list.add(arr[i]);
        }
        Collections.sort(list, Collections.reverseOrder());
        for (int i = 0; i < n; i++) {
            arr[i] = list.get(i);
        }
    }

    private void rsort(int[] arr) {
        int n = arr.length;
        List<Integer> list = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            list.add(arr[i]);
        }
        Collections.sort(list, Collections.reverseOrder());
        for (int i = 0; i < n; i++) {
            arr[i] = list.get(i);
        }
    }

    private void sort(long[] arr) {
        int n = arr.length;
        List<Long> list = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            list.add(arr[i]);
        }
        Collections.sort(list);
        for (int i = 0; i < n; i++) {
            arr[i] = list.get(i);
        }
    }

    private void rsort(long[] arr) {
        int n = arr.length;
        List<Long> list = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            list.add(arr[i]);
        }
        Collections.sort(list, Collections.reverseOrder());
        for (int i = 0; i < n; i++) {
            arr[i] = list.get(i);
        }
    }
    //---------------------------------------power----------------------------------------------------//

    public long pow(long a, int b) {
        long ans = 1L;
        while (b > 0) {
            if ((b & 1) > 0) {
                ans *= a;
            }
            a *= a;
            b >>= 1;
        }
        return b;
    }
    //----------------------------------------binary_exponentiation-----------------------------------//

    public long exp(long a, long b, long mod) {
        long ans = 1L;
        while (b > 0) {
            if ((b & 1) > 0) {
                ans = (ans * a) % mod;
            }
            a = (a * a) % mod;
            b >>= 1;
        }
        return ans;
    }
    int t;
    public void solve() throws IOException {
        t = sc.nextInt();
        while (t-- > 0) {
            int n = i();
            List<Set<Integer>> a = new ArrayList<>();
            int[][] in = new int[n+1][2];
            for(int i =0;i<=n;i++){
                a.add(new HashSet<>());
                in[i][1] = i;
            }
            for(int i = 1;i<n;i++){
                int x = i(), y = i();
                a.get(x).add(y);
                a.get(y).add(x);
                in[x][0]++; in[y][0]++;
            }
            Arrays.sort(in, (x, y) -> y[0] - x[0]);
            int ans = 0;
            for(int i = 1;i<=n;i++){
                for(int e: a.get(i)){
                    ans = max(ans, a.get(i).size() + a.get(e).size() - 2);
                }
            }
            for(int i = 0;i<n;i++){
                for(int j = i+1;j<n;j++){
                    if(a.get(in[i][1]).contains(in[j][1])) continue;
                    ans = max(ans, in[i][0] + in[j][0] - 1);
                    break;
                }
            }
            out.print(ans);
            out.print("\n");
        }
    }
}