[leetcode]202. Happy Number

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

class Solution {public:    bool isHappy(int n) {        if(n<1)            return false;        if(n==1)            return true;        int num[10];        int tmp[100];        tmp[0] = n;        int no = 1;                while(1)        {            int length = 0;            while(n>=1)            {                num[length]=n%10;                length++;                n = n/10;            }            int bak = 0;            for(int i=0; i<length; i++)                bak += num[i] * num[i];            if(bak==1)                return true;            for(int i=0; i<no; i++)            {                if(bak==tmp[i])                    return false;            }            tmp[no] = bak;            no++;            n = bak;        }    }};

我的思路：

①判断特殊情况，n<1肯定是不符合条件的，要求是一个正数；n=1不需要做判断

②判断一般情况。int型的十进制形式最高只占10位，申请数组num[10]，功能是存放每位的数值。length计算num里面数据存储了几位；bak作为一个备份，存放新更新的n；tmp[100]存放不属于1的bak值，并判断是否有cycle