Happy Number

描述

Write a function to determine if a number is "happy number".

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

$1^2 + 9^2 = 82$

$8^2 + 2^2 = 68$

$6^2 + 8^2 = 100$

$1^2 + 0^2 + 0^2 = 1$

分析

这题找到规律后就简单了。如果右边的出现了某个重复的数，但不是1，说明会无限循环下去，这个数就不是快乐数，如果是1，则是快乐数。

代码

原文: https://soulmachine.gitbooks.io/algorithm-essentials/content/cpp/number-theory/happy-number.html