914.X of a Kind in a Deck of Cards

Tags: Easy Array Math

Links: https://leetcode.com/problems/x-of-a-kind-in-a-deck-of-cards/

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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

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class Solution {
public:
    bool hasGroupsSizeX(vector<int>& deck) {
        std::ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        cout.tie(NULL);

        if (deck.size() == 1) return false;

        unordered_map<int, int> um;
        vector<int> num;
        for (auto e : deck) ++um[e];
        for (auto e : um) num.push_back(e.second);

        int n = num.size();
        int res = num[0];
        for (int i = 1; i < n; ++i) {
            res = GCD(res, num[i]);
            if (res == 1) return false;
        }

        return true;
    }

    inline int GCD(int a, int b)
    {
        return b == 0 ? a : GCD(b, a % b);
    }
};