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  1. import java.util.*;
  2. import java.util.stream.*;
  3.  
  4. class FastFactoring
  5. {
  6. 	public static void main (String[] args)
  7. 	{
  8. 		long num = Integer.MAX_VALUE;
  9. 		Map<Long, Integer> factors = factorize(num);
  10.  
  11. 		//Printing out the map...
  12. 		System.out.printf("%d = ", num);
  13.             if (factors.get(num) != null) {
  14.                 System.out.print("PRIME");
  15.             } else {
  16.                 Iterator<Long> factorKeys = factors.keySet().iterator();
  17.                 for (int j = 0; j < factors.size(); j++) {
  18.                     long factor = factorKeys.next();
  19.                     int count = factors.get(factor);
  20.                     if (count > 1) {
  21.                         System.out.printf("%d^%d", factor, count);
  22.                     } else {
  23.                         System.out.printf("%d", factor);
  24.                     }
  25.                     if (j + 1 != factors.size()) {
  26.                         System.out.print("×");
  27.                     }
  28.                 }
  29.             }
  30.             System.out.println();
  31. 	}
  32.  
  33. 	public static Map<Long, Integer> factorize(long num) {
  34.         Map<Long, Integer> factors = new LinkedHashMap<>();
  35.         long n = num;
  36.         for (long i = 2; i <= n / i; i++) {
  37.             int count = 0;
  38.             while (n % i == 0) {
  39.                 count++;
  40.                 n /= i;
  41.             }
  42.             if (count > 0) {
  43.                 factors.put(i, count);
  44.  
  45.             }
  46.         }
  47.         if (n > 1) {
  48.             factors.put(n, 1);
  49.         }
  50.         return factors;
  51.     }
  52. }
Success #stdin #stdout 0.11s 321280KB
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2147483647 = PRIME
https://ideone.com/pdshk6
language:
Java (HotSpot 12)
created:
9 years ago
visibility:
public

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