LeetCode 202. Happy Number

Description

https://leetcode.com/problems/happy-number/

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

Explanation

Use a hashmap to check if the number gets a cycle.

Python Solution

class Solution:
    def isHappy(self, n: int) -> bool:
        visited = {}
        
        return self.is_happy_helper(n, visited)
        
    def is_happy_helper(self, n, visited):
        
        if n == 1:
            return True
        
        digits_sum = 0
        while n != 0:
            digit = n % 10
            digits_sum += digit**2
            n = n // 10
            
        if digits_sum not in visited:
            visited[digits_sum] = 1
        else:
            return False

        return self.is_happy_helper(digits_sum, visited)
  • Time complexity: O(n).
  • Space complexity: O(n).

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