leetcode 202-- Happy number

link ： Happy number

Title Description

Thought analysis

1、 First of all, we need to understand the meaning of the topic , That is, the given number can be squared according to its ten hundred .
2、 If the number after the square turns out to be 1, Then this number is happy number .
3、 If duplicate numbers appear in the final result , Then this number is not a happy number , How to judge whether the numbers are repeated , It must pass hashset.

Code demonstration

class Solution {
    public boolean isHappy(int n) {
        HashSet<Integer> hashSet = new HashSet<>();

        while (n != 1 && !hashSet.contains(n)){
            hashSet.add(n);
            n = getNextnumber(n);
        }

        return n == 1;
    }

    public int getNextnumber(int n){
        int res = 0;
        while(n > 0){
            int tem = n % 10;
            res += tem*tem;
            n = n / 10; 
        }
        return res;
    }
}