[LeetCode202] Happy Number

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

Solution:

use loop to calcuate the square sum until meet one of these two stops:

1. sum is 1, return true

2. sum value got before, which means there is a sum loop and will never goes to 1. return false 

public boolean isHappy(int n) {
        if(n<=0) return false;
        Set<Long> records = new HashSet<>();
        long ln = n;
        while(ln< Integer.MAX_VALUE){
            if(records.contains(ln)) return false;
            else records.add(ln);
            ln = getSquareSum(ln);
            if(ln == 1) return true;
        }
        return false;
    }
    public long getSquareSum(long n){
        long sum = 0;
        while(n!=0){
            sum+= Math.pow(n%10,2);
            n/=10;
        }
        return sum;
    }