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  1. import java.io.BufferedReader;
  2. import java.io.InputStreamReader;
  3. import java.io.IOException;
  4. import java.lang.NumberFormatException;
  5. import java.util.ArrayList;
  6. import java.util.function.Predicate;
  7.  
  8. class Collatz {
  9.     public static void main (String[] args) throws NumberFormatException {
  10.         int n = 0;
  11.         try {
  12.             BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
  13.             do {
  14.                 System.out.print("Enter an integer greater than 0: ");
  15.                 n = Integer.parseInt(br.readLine());
  16.             } while (n <= 0);
  17.         } catch (IOException | NumberFormatException e){
  18.             System.err.println("Caught exception " + e.getMessage());
  19.             System.exit(1);
  20.         }
  21.         System.out.format("The Collatz sequence starting from %d", n);
  22.         ArrayList<Integer> collatz = new ArrayList<>();
  23.         while (n > 1) {
  24.             collatz.add(n);
  25.             if ((n % 2) == 0)
  26.                 n /= 2;
  27.             else
  28.                 n = (3 * n) + 1;
  29.         }
  30.         collatz.add(n);
  31.         System.out.format(" has %d elements.%n", collatz.size());
  32.         Predicate<Integer> isEvenNumber = e -> e % 2 == 0;
  33.         Predicate<Integer> isOddNumber = o -> o % 2 != 0;
  34.         System.out.format("There are %d even numbers and %d odd numbers",
  35.                 collatz.stream().filter(isEvenNumber).count(),
  36.                 collatz.stream().filter(isOddNumber).count());
  37.     }
  38. }
Success #stdin #stdout 0.12s 56356KB
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stdin
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7
stdout
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Enter an integer greater than 0: The Collatz sequence starting from 7 has 17 elements.
There are 11 even numbers and 6 odd numbers
https://ideone.com/uE2ecM
language:
Java (HotSpot 12)
created:
4 days ago
visibility:
public

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