Submission #5500072

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Source Code Expand

import java.util.Arrays;

public class Main {
  private static void solve() {
    int n = ni();
    int[] from = new int[n-1];
    int[] to = new int[n-1];
    for (int i = 0; i < n - 1; i ++) {
      from[i] = ni() - 1;
      to[i] = ni() - 1;
    }
    int[][] g = packU(n, from, to);
    
    int dia = diameter(g)[0];
    
    int now = 0;
    for (int k = 0;; k ++) {
      if (now >= dia) {
        System.out.println(k);
        return;
      }
      now = now * 2 + 2;
    }
  }
  
  public static int[][] packU(int n, int[] from, int[] to){ return packU(n, from, to, from.length); }
  public static int[][] packU(int n, int[] from, int[] to, int sup)
  {
      int[][] g = new int[n][];
      int[] p = new int[n];
      for(int i = 0;i < sup;i++)p[from[i]]++;
      for(int i = 0;i < sup;i++)p[to[i]]++;
      for(int i = 0;i < n;i++)g[i] = new int[p[i]];
      for(int i = 0;i < sup;i++){
          g[from[i]][--p[from[i]]] = to[i];
          g[to[i]][--p[to[i]]] = from[i];
      }
      return g;
  }

  
  public static int[] diameter(int[][] g)
  {
      int n = g.length;
      int f0 = -1, f1 = -1, d01 = -1;
      int[] q = new int[n];
      boolean[] ved = new boolean[n];
      {
          int qp = 0;
          q[qp++] = 0; ved[0] = true;
          for(int i = 0;i < qp;i++){
              int cur = q[i];
              for(int e : g[cur]){
                  if(!ved[e]){
                      ved[e] = true;
                      q[qp++] = e;
                      continue;
                  }
              }
          }
          f0 = q[n-1];
      }
      {
          int[] d = new int[n];
          int qp = 0;
          Arrays.fill(ved, false);
          q[qp++] = f0; ved[f0] = true;
          for(int i = 0;i < qp;i++){
              int cur = q[i];
              for(int e : g[cur]){
                  if(!ved[e]){
                      ved[e] = true;
                      q[qp++] = e;
                      d[e] = d[cur] + 1;
                      continue;
                  }
              }
          }
          f1 = q[n-1];
          d01 = d[f1];
      }
      return new int[]{d01, f0, f1};
  }
  public static void main(String[] args) {
    new Thread(null, new Runnable() {
      @Override
      public void run() {
        long start = System.currentTimeMillis();
        String debug = args.length > 0 ? args[0] : null;
        if (debug != null) {
          try {
            is = java.nio.file.Files.newInputStream(java.nio.file.Paths.get(debug));
          } catch (Exception e) {
            throw new RuntimeException(e);
          }
        }
        reader = new java.io.BufferedReader(new java.io.InputStreamReader(is), 32768);
        solve();
        out.flush();
        tr((System.currentTimeMillis() - start) + "ms");
      }
    }, "", 64000000).start();
  }

  private static java.io.InputStream is = System.in;
  private static java.io.PrintWriter out = new java.io.PrintWriter(System.out);
  private static java.util.StringTokenizer tokenizer = null;
  private static java.io.BufferedReader reader;

  public static String next() {
    while (tokenizer == null || !tokenizer.hasMoreTokens()) {
      try {
        tokenizer = new java.util.StringTokenizer(reader.readLine());
      } catch (Exception e) {
        throw new RuntimeException(e);
      }
    }
    return tokenizer.nextToken();
  }

  private static double nd() {
    return Double.parseDouble(next());
  }

  private static long nl() {
    return Long.parseLong(next());
  }

  private static int[] na(int n) {
    int[] a = new int[n];
    for (int i = 0; i < n; i++)
      a[i] = ni();
    return a;
  }

  private static char[] ns() {
    return next().toCharArray();
  }

  private static long[] nal(int n) {
    long[] a = new long[n];
    for (int i = 0; i < n; i++)
      a[i] = nl();
    return a;
  }

  private static int[][] ntable(int n, int m) {
    int[][] table = new int[n][m];
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < m; j++) {
        table[i][j] = ni();
      }
    }
    return table;
  }

  private static int[][] nlist(int n, int m) {
    int[][] table = new int[m][n];
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < m; j++) {
        table[j][i] = ni();
      }
    }
    return table;
  }

  private static int ni() {
    return Integer.parseInt(next());
  }

  private static void tr(Object... o) {
    if (is != System.in)
      System.out.println(java.util.Arrays.deepToString(o));
  }
}

Submission Info

Judge Result