# LeetCode 202. Happy Number

Created at 2018-01-23 Updated at 2018-01-23 Category LeetCode Tag LeetCode

## 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

• 1^2 + 9^2 = 82
• 8^2 + 2^2 = 68
• 6^2 + 8^2 = 100
• 1^2 + 0^2 + 0^2 = 1

## Solution

• HashTable

Since this problem is a question tagged with HashTable, using hash table can solve this kind of problem.

Get the sum of the squares of the input number’s digits. If it equals to 1 then return True, no doubt it is a happy number, else store it in a hash table. If the hash table has stored it, return False.

Aparently, we can transfer this problem into a detecting cycled link list porblem by using a fast and a slow pointer.

• HashTable

## Table of Content

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