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].

Example 2:

Input: deck = [1,1,1,2,2,2,3,3]
Output: false´
Explanation: No possible partition.

Example 3:

Input: deck = [1]
Output: false
Explanation: No possible partition.

Example 4:

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

Example 5:

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

Constraints:

• 1 <= deck.length <= 10^4

• 0 <= deck[i] < 10^4

class Solution {
    public int gcd(int x, int y) {
        if (y == 0)
            return x;
        if (y > x)
            return gcd(y, x);
        return gcd(y, x % y);
    }

    public boolean hasGroupsSizeX(int[] deck) {
        if (deck.length == 1)
            return false;
        Map<Integer, Integer> map = new HashMap<>();
        for (int x : deck)
            map.put(x, map.getOrDefault(x, 0) + 1);
        if (map.size() == 1)
            return true;
        int gcd = 1, index = 0;
        boolean first = true;
        int[] numbers = new int[map.size()];
        for (int x : map.keySet())
            numbers[index++] = x;
        for (int i = 1; i < numbers.length; i++) {
            if (first) {
                gcd = gcd(map.get(numbers[i]), map.get(numbers[i - 1]));
                first = false;
            } else
                gcd = gcd(gcd, map.get(numbers[i]));
        }
        return gcd >= 2;
    }
}