Problem
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:
Input: 19
Output: true
Explanation:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1
Notes
Hash Table
Solution
class Solution:
def isHappy(self, n):
table = {}
while n != 1:
x = n
n = 0
while x != 0:
n += (x % 10)**2
x //= 10
if table.get(n):
return False
else:
table[n] = 1
return True
class Solution:
def isHappy(self, n):
mem = set()
while n not in mem:
mem.add(n)
n = sum(int(i)**2 for i in str(n))
return n == 1