[LeetCode] Problem 202 - Happy Number

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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

Input: 19

Output: true

Explanation: 

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1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1

Code

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public boolean isHappy(int n) {
    HashSet<Integer> set = new HashSet<>();

    while (n != 1) {
        if (set.contains(n))
            return false;

        set.add(n);
        n = sum(n);
    }

    return true;
}

private int sum(int n) {
    int sum = 0;

    while (n != 0) {
        sum += Math.pow(n % 10, 2);
        n /= 10;
    }

    return sum;
}