LeetCode 202. Happy Number
Created at 20180123 Updated at 20180123 Category 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
.
 Detecting Cycled Link
Aparently, we can transfer this problem into a detecting cycled link list porblem by using a fast and a slow pointer.
Code
 HashTable


 Detecting Cycled LinkList

