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: [1,2,3,4,4,3,2,1]
Output: true
Explanation: Possible partition [1,1],[2,2],[3,3],[4,4]

Example 2:

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

Example 3:

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

Example 4:

Input: [1,1]
Output: true
Explanation: Possible partition [1,1]

Example 5:

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

Note:

1. 1 <= deck.length <= 10000
2. 0 <= deck[i] < 10000

Approach #1: Array + GCD. [Java]

class Solution {
    public boolean hasGroupsSizeX(int[] deck) {
        int res = 0;
        Map<Integer, Integer> map = new HashMap<>();
        for (int d : deck) map.put(d, map.getOrDefault(d, 0) + 1);
        for (int m : map.values()) res = gcd(res, m);
        return res > 1;
    }
    public int gcd(int x, int y) {
        return y > 0 ? gcd(y, x % y) : x;
    }
}

　　

Reference:

https://leetcode.com/problems/x-of-a-kind-in-a-deck-of-cards/discuss/175845/C%2B%2BJavaPython-Greatest-Common-Divisor