問題描述：

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.

19 is a happy number

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

問題分析：

非happy數會有一個特點，在迴圈過程中會出現4這個值，依次我們只需要將1和4作為跳出迴圈的條件即可。

過程詳見程式碼：

class Solution {
public:
    bool isHappy(int n) {
        while(n != 1 && n != 4)
        {
        	int t = 0;
        	while(n)
        	{
				t += (n % 10) * (n % 10);
				n /= 10;
			}
			n = t;
		}
		return n == 1;
    }
};