Happy_Number.py

# 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

# solution
class Solution:
  def isHappy(self, n: int) -> bool:
    def squaredSum(n: int) -> bool:
      summ = 0
      while n:
        summ += pow(n % 10, 2)
        n //= 10
      return summ

    slow = squaredSum(n)
    fast = squaredSum(squaredSum(n))

    while slow != fast:
      slow = squaredSum(slow)
      fast = squaredSum(squaredSum(fast))

    return slow == 1