LeetCode 202 Happy Hour

Link: https://leetcode.com/problems/happy-number/

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: 19 is a happy number

  • 12 + 92 = 82
  • 82 + 22 = 68
  • 62 + 82 = 100
  • 12 + 02 + 02 = 1

Solution1:

public class happy {
    public static boolean isHappy(int n) {
        int sum = 0;
        int div = 10;
        int mod = 10;
        while(n>0) {
            int tmp = n%mod;
            System.out.print(tmp+"\t");
            sum += tmp*tmp;
            n /= div;
        }
        if(sum == 1) {return true;}
        else {
            return isHappy(sum);
        }
    }

    public static void main(String[] args) {
        isHappy(7);
    }
}

Solution2:

    public static boolean isHappy1(int n){
        int newN = 0;
        HashSet set = new HashSet();
        while(!set.contains(n)) {
            set.add(n);
            newN = 0;
            while(n != 0) {
                newN += (n%10) * (n%10);
                n /= 10;
            }
            n = newN;
            System.out.print(n+"\t");
            if(n==1) return true;
        }
        return false;
    }
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