[LC] 914. X of a Kind in a Deck of Cards

In a deck of cards, each card has an integer written on it.

Return true if and only if you can choose X >= 2 such that it is possible to split the entire deck into 1 or more groups of cards, where:

• Each group has exactly X cards.
• All the cards in each group have the same integer.

Example 1:

Input: deck = [1,2,3,4,4,3,2,1]
Output: true
Explanation: Possible partition [1,1],[2,2],[3,3],[4,4].

class Solution {
    public boolean hasGroupsSizeX(int[] deck) {
        Map<Integer, Integer> map = new HashMap<>();
        for (int num : deck) {
            map.put(num, map.getOrDefault(num, 0) + 1);
        }
        int res = 0;
        for (Map.Entry<Integer, Integer> entry: map.entrySet()) {
            res = getGCD(entry.getValue(), res);
        }
        return res > 1;
    }
    
    private int getGCD(int a, int b) {
        if (a == 0) {
            return b;
        }
        return getGCD(b % a, a);
    }
}