## Happy Number

07/16/2016 Hash Table Math

## Question

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

## Solution

Result: Accepted Time: 52 ms

Here should be some explanations.

class Solution(object):
def isHappy(self, n):
"""
:type n: int
:rtype: bool
"""
st=set()
while n not in st:
sum = 0
last  = n
while n:
tmp = n % 10;
sum += tmp * tmp
n /= 10

• Time Complexity: $O(n)$
• Space Complexity: $O(1)$