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: 19 is a happy number

• 1² + 9² = 82
• 8² + 2² = 68
• 6² + 8² = 100
• 1² + 0² + 0² = 1

Code:

 bool isHappy(int n) {
        /*这道题的核心问题在于怎么判断是否为死循环。可以考虑：如果重复出现一个数字则说明将陷入死循环
        一个int型数据经计算后的最大值为9*9*10=810.因此有810个数据需要记录。
        备注：刚开始，有想到这个思路，但是没有分析到一个int型数据经计算后的最大值为9*9*10=810，所需空间并没有想象中那么大。
        */
        int result = 0;
        int data[1000] = {0};
        while (1)
        {
            result = 0;
            while (n)
            {
                result += (n%10)*(n%10);
                n = n/10;
            }
            if (result == 1)
                return true;
            else
            {
                if (data[result] == 1)
                    return false;
                else
                    data[result] = 1;
            }
            n = result;
        }
    }

 PS:

16位整数:-32768到32767

32位整数中:-2147483648到2147 483 647