[leetcode] 202. Happy Number

[leetcode] 202. Happy Number

Description

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: 19Output: trueExplanation: 1^2 + 9^2 = 828^2 + 2^2 = 686^2 + 8^2 = 1001^2 + 0^2 + 0^2 = 1

分析

题目的意思是：判断一个数是否是开心数。

这是leetcode上的easy题目。关键是怎么判断循环的存在，这里用了一个set存放已经出现过的数字，所以后面只需要判断数字在set是否出现过就可以判断是否有循环了，如果有循环，则数字一定会在set里面再出现，这样就找到了终止条件了。

代码

class Solution {public: bool isHappy(int n) { set s; while(n!=1){ int t=0; while(n>0){ t+=(n%10)*(n%10); n=n/10; } n=t; if(s.count(t)){ break; }else{ s.insert(t); } } return n==1; }};

参考文献

​​[LeetCode] Happy Number 快乐数​​

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