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  1. // Java program to answer
  2. // queries for frequencies
  3. // in O(1) time.
  4.  
  5. import java.io.*;
  6. import java.util.*;
  7.  
  8. class GFG {
  9.  
  10. static HashMap <Integer, Integer> hm = new HashMap<Integer, Integer>();
  11.  
  12. static void countFreq(int a[], int n)
  13. {
  14. 		// Insert elements and their
  15. 		// frequencies in hash map.
  16. 		for (int i=0; i<n; i++)
  17. 			if (hm.containsKey(a[i]) )
  18. 				hm.put(a[i], hm.get(a[i]) + 1);
  19. 			else hm.put(a[i] , 1);
  20. 	}
  21.  
  22. 	// Return frequency of x (Assumes that
  23. 	// countFreq() is called before)
  24. 	static int query(int x)
  25. 	{
  26. 		if (hm.containsKey(x))
  27. 			return hm.get(x);
  28. 		return 0;
  29. 	}
  30.  
  31. 	// Driver program
  32. 	public static void main (String[] args) {
  33. 		int a[] = {1, 3, 2, 4, 2, 1};
  34. 		int n = a.length;
  35. 		countFreq(a, n);
  36. 		System.out.println(query(2));
  37. 		System.out.println(query(3));
  38. 		System.out.println(query(5));
  39. 	}
  40. 	}
  41.  
Success #stdin #stdout 0.07s 52540KB
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https://ideone.com/6MUeIl
language:
Java (HotSpot 12)
created:
13 days ago
visibility:
public

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