202. Happy Number

Write an algorithm to determine if a number n 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.
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.

Return true if n is a happy number, and false if not.

Example 1:

Input: n = 19
Output: true
Explanation:
1² + 9² = 82
8² + 2² = 68
6² + 8² = 100
1² + 0² + 0² = 1

Example 2:

Input: n = 2
Output: false

Constraints:

1 <= n <= 2³¹ - 1

Source

Code

In [1]:

def is_happy(n): 
    visited = set()
    while n not in visited:
        visited.add(n)
        n = sum([int(x) **2 for x in str(n)])
    return n == 1

In [2]:

def is_happy(n):
    '''variations from above solution'''
    visited = set()
    while n != 1:
        n = sum([int(i)**2 for i in str(n)])
        if n in visited:
            return False
        visited.add(n)
    return True

Check

In [3]:

is_happy(19)

Out[3]:

True

In [4]:

is_happy(2)

Out[4]:

False

In [5]:

is_happy(3)

Out[5]:

False