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