202. Happy Number

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: 19 is a happy number

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

Hide Tags

 Hash Table Math

Hide Similar Problems

 (E) Add Digits (E) Ugly Number

 

public class Solution {
    public boolean isHappy(int n) {
        HashSet<Integer> set = new HashSet<Integer>();
        int sum = 0;
        while(true)
        {
            if(n == 1)
                return true;
            while(n>0)
            {
                int r = n%10;
                sum += r*r;
                n = n/10;
            }
            if(!set.add(sum))
                return false;
            n = sum;
            sum = 0;
        }
    }
}

 

We can also use faster and slower pointer to detect cycle.