python快乐数字_LeetCode 202. Happy Number（快乐数）

题目描述

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

解法一

思路

“求一个数的所有数字的平方和”挺简单的：

按照题目的描述，需要循环求平方和，即求出当前数组的平方和后，再以此平方和作为新的数继续求平方和，而循环终止条件是：得到的平方和为1，或得到的平方和在之前的循环中出现过。判断平方和是否为1很简单，每次检查就好了；而判断平方和是否出现过，则只需要维持一个Set，每次循环检查当前平方和是否在Set中，在则终止循环，不在则将此平方和放到Set中。

Python

Java

C++