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

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1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1

Solution

• Use hash_table to record each number

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class Solution(object):
    def isHappy(self, n):
        """
        :type n: int
        :rtype: bool
        """
        if n <=0:
            return False
        hash_table = dict()
        while True:
            if n == 1:
                return True
            hash_table[n] = 1

            n = sum([int(x)*int(x) for x in list(str(n))])
            if n in hash_table:
                return False