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  1. import java.io.BufferedReader;
  2. import java.io.InputStreamReader;
  3. import java.util.ArrayDeque;
  4. import java.util.HashSet;
  5. import java.util.Queue;
  6.  
  7.  
  8.  
  9.  
  10.  
  11. class PT07Z2
  12. {  static int pop;
  13.     static  boolean marked[];
  14.  
  15.  
  16.   static int dist;
  17.  
  18. public static void main(String args[]) 
  19. {   try {
  20.     int a,b,n;
  21.         BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
  22.         int node=n=Integer.parseInt(br.readLine());
  23.         HashSet<Integer>[] hs=new HashSet[node];
  24.         for(int i = 0; i < node; i++){
  25.             hs[i] = new HashSet<>();
  26.         }      
  27.         marked= new boolean[node];
  28. Queue<Integer> popper= new ArrayDeque<>();
  29.         while(node>1)
  30.         {
  31.             String str[]=br.readLine().split(" ");
  32.             a=Integer.parseInt(str[0]);
  33.             b=Integer.parseInt(str[1]);
  34.             hs[a-1].add(b-1);
  35.             hs[b-1].add(a-1);
  36.             node--;
  37.         }  
  38.         popper.add(0);
  39.     int present_level=1;
  40.         int next_level=0;
  41.         int from=  bfs(popper,  hs,present_level,next_level);
  42.         popper.add(from);
  43.         marked= new boolean[n];
  44.         dist=0;
  45.         present_level=1;
  46.         next_level=0;
  47.       int to=bfs(popper, hs,present_level,next_level);
  48.         System.out.println(dist-1);
  49.     } catch (Exception e) {
  50.        System.out.println(e);
  51.  
  52.  
  53.     }
  54. }
  55. static int bfs(Queue<Integer> popper, HashSet<Integer>[] l,int pl,int nl)
  56. { 
  57.  pop=popper.remove();
  58.  pl--;
  59.  
  60.  
  61.  
  62. marked[pop]=true;
  63. for(int i:l[pop])
  64.     if(marked[i]==false)
  65.     {
  66.  
  67.         popper.add(i);
  68.         nl++;
  69.  
  70.  
  71.     }
  72.  
  73. if(pl==0)
  74. {pl=nl;
  75.  
  76.  
  77. nl=0;
  78. dist++;
  79. }   
  80.  
  81.     if(!popper.isEmpty())
  82.     bfs(popper, l,pl,nl);
  83.  
  84.  
  85. return pop;
  86. }
  87. }
Success #stdin #stdout 0.1s 320256KB
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Standard input is empty
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java.lang.NumberFormatException: null
https://ideone.com/LWSsEj
language:
Java (HotSpot 12)
created:
9 years ago
visibility:
public

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