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
快乐数有以下的特性:在给定的进位制下,该数字所有数位(digits)的平方和,得到的新数再次求所有数位的平方和,如此重复进行,最终结果必为1。
非快乐数有以下的特性:所有不快乐数的数位平方和计算,最後都会进入 4 → 16 → 37 → 58 → 89 → 145 → 42 → 20 → 4 的循环中。
所以外层循环:判断是否为快乐数和非快乐数。内层循环对n进行快乐数分解计算。
class Solution { public: bool isHappy(int n) { while (n != 1 && n != 4) { int sum = 0, tmp = 0; while (n != 0) { tmp = n % 10; sum += tmp * tmp; n /= 10; } n = sum; } return n == 1; } }; // 3 ms