LeetCode – Happy Number (Java)

Write an algorithm to determine if a number is "happy".

What is an happy number can be shown in the following 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


The key to solve this problem is the stop condition for the loop.

Java Solution

public boolean isHappy(int n) {
    HashSet<Integer> set = new HashSet<Integer>();
        n = getSum(n);
            return true;
    return false;
public int getSum(int n){
    int sum =0;
    return sum;    
Category >> Algorithms >> Interview  
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  • Captain Guintu

    We need a set because we know it will not be a happy number if it’ll return to a previous sum we’ve seen before. This basically means it will run in a continuous loop. A hash could also be used to store the sums previously seen for O(1) lookup time.

  • Kshama Dalal

    Why do we need set?

  • Kai Li