202.happy-number.java

/*
 * @lc app=leetcode id=202 lang=java
 *
 * [202] Happy Number
 *
 * https://leetcode.com/problems/happy-number/description/
 *
 * algorithms
 * Easy (46.28%)
 * Likes:    998
 * Dislikes: 264
 * Total Accepted:    260.4K
 * Total Submissions: 561.6K
 * Testcase Example:  '19'
 *
 * Write an algorithm to determine if a number is "happy".
 *
 * A happy number is a number defined by the following process: Starting with
 * any positive integer, replace the number by the sum of the squares of its
 * digits, and repeat the process until the number equals 1 (where it will
 * stay), or it loops endlessly in a cycle which does not include 1. Those
 * numbers for which this process ends in 1 are happy numbers.
 *
 * Example: 
 *
 *
 * Input: 19
 * Output: true
 * Explanation:
 * 1^2 + 9^2 = 82
 * 8^2 + 2^2 = 68
 * 6^2 + 8^2 = 100
 * 1^2 + 0^2 + 0^2 = 1
 *
 */
class Solution {
  public boolean isHappy(int n) {
    Set<Integer> set = new HashSet<>();
    while (n != 1 && !set.contains(n)) {
      set.add(n);
      n = sumOfDigits(n);
    }
    return (n == 1) ? true : false;
  }

  public int sumOfDigits(int n) {
    int sum = 0;
    while (n != 0) {
      sum += (n%10) * (n%10);
      n /= 10;
    }
    return sum;
  }
}