Leetcode 快乐数Happy Number

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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
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1
一开始的想法就是直接按定义来：

int getsum(int x){int sum=0;while(x){sum+=(x%10)*(x%10);x=x/10;}return sum;}bool isHappy(int n) {    if(n<=0)return false;bool f=1;long k=getsum(n);while(k!=1){f=0;k=getsum(k);}if(f==0)return true;else return false;}

最后发现运行时间够长，Time Limit Exceeded

最终查阅有关快来数定义，发现当在迭代循环判断是否为1的过程中时，若进入了这种无限循环，最终都会出现4，故一旦遇见4即可知道进入了无限循环，判断是非快乐数字，减少了时间复杂度：

int getsum(int x){int sum=0;while(x){sum+=(x%10)*(x%10);x=x/10;}return sum;}bool isHappy(int n) {    if(n<=0)return false;while(n!=1){n=getsum(n);if(n==4)return false;}return true;}

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