HappyNumber.java

package com.examplehub.leetcode.easy;

import java.util.HashSet;
import java.util.Set;

public class HappyNumber {

  private static int getNex(int number) {
    int sum = 0;
    while (number != 0) {
      int remainder = number % 10;
      sum += remainder * remainder;
      number /= 10;
    }
    return sum;
  }

  public static boolean solution1(int number) {
    Set<Integer> set = new HashSet<>();
    while (number != 1 && !set.contains(number)) {
      set.add(number);
      number = getNex(number);
    }
    return number == 1;
  }

  public static boolean solution2(int number) {
    int slowRunner = number;
    int fastRunner = getNex(number);
    while (slowRunner != 1 && slowRunner != fastRunner) {
      slowRunner = getNex(slowRunner);
      fastRunner = getNex(getNex(fastRunner));
    }
    return slowRunner == 1;
  }
}