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  1. import java.util.*;
  2. import java.lang.*;
  3. import java.io.*;
  4.  
  5. class Codechef
  6. {
  7. 	public static void main (String[] args) throws java.lang.Exception
  8. 	{
  9. 	    /*
  10. 	        number of unordered quadruplets (i,j,k,l) such that b[i] + b[j] + b[k] + b[l] = 0
  11.  
  12. 	    */
  13.  
  14.  
  15. 	    //O(n^4) ;
  16. 	    Scanner sc = new Scanner(System.in) ; 
  17. 	    int n = sc.nextInt() ; 
  18. 	    int arr[] = new int[n] ; 
  19.  
  20. 	    for(int i = 0 ; i < n ; i++) {
  21. 	        arr[i] = sc.nextInt() ; 
  22. 	    }
  23.  
  24.  
  25. 	    Map<Integer , Integer > map = new HashMap<>() ; 
  26.  
  27. 	    for(int i = 2 ; i < n ; i++) {
  28. 	        for(int j = i + 1 ; j < n ; j++) {
  29. 	            map.put(arr[i] + arr[j] , map.getOrDefault(arr[i] + arr[j] , 0) + 1) ; 
  30. 	        }
  31. 	    }
  32. 	    int count = 0 ;
  33.  
  34.  
  35. 	   for(int i = 1 ; i < n - 1; i++) {
  36. 	       for(int j = 0 ; j < i ; j++  ) {
  37. 	           int sum = 0 - (arr[i] + arr[j] ); 
  38. 	           if(map.containsKey(sum)) {
  39. 	               count += map.get(sum) ; 
  40. 	           }
  41. 	       }
  42.  
  43. 	       for(int k = i + 2 ; k < n ; k++) { //remove pair for that element wich is going to become i next 
  44. 	           map.put(arr[i+1] + arr[k] , map.get(arr[i+1] + arr[k] ) - 1 ) ; 
  45. 	       }
  46. 	   }
  47.  
  48. 	    System.out.println(count);
  49. 	}
  50. }
  51.  
Runtime error #stdin #stdout #stderr 0.18s 54468KB
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stdin
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Standard input is empty
stdout
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Standard output is empty
stderr
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Exception in thread "main" java.util.NoSuchElementException
	at java.base/java.util.Scanner.throwFor(Scanner.java:937)
	at java.base/java.util.Scanner.next(Scanner.java:1594)
	at java.base/java.util.Scanner.nextInt(Scanner.java:2258)
	at java.base/java.util.Scanner.nextInt(Scanner.java:2212)
	at Codechef.main(Main.java:17)
https://ideone.com/NBp5ny
language:
Java (HotSpot 12)
created:
145 days ago
visibility:
secret

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