Happy Number 488

Question

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

1^2 + 9^2 = 82

8^2 + 2^2 = 68

6^2 + 8^2 = 100

1^2 + 0^2 + 0^2 = 1

Solution

将每一位的平方相加得到一个新的数n，用一个HashSet记录所有曾经得到过的数。若有重复，则返回false。

代码如下：

public class Solution {
    /**
     * @param n an integer
     * @return true if this is a happy number or false
     */
    public boolean isHappy(int n) {
        // Write your code here
        if(n == 0){
            return false;
        }

        HashSet<Integer> nums = new HashSet<Integer>();

        while(n != 1){
            if(nums.contains(n)){
                return false;
            }
            nums.add(n);
            int sum = 0;
            while(n !=0){
                sum += (n % 10) * (n % 10);
                n = n / 10;
            }
            n = sum;
        }

        return true;
    }
}