Is X of a Kind in a Deck of Cards easy or hard?

The problem is rated Easy on LeetCode but requires recognizing the GCD insight. Many beginners attempt brute-force grouping checks first. Once you realize that all frequencies must share a common divisor greater than 1, the solution becomes straightforward.

How to solve X of a Kind in a Deck of Cards in O(n)?

Count the frequency of each card using a hash map. Then compute the GCD of all frequency values. If the resulting GCD is greater than or equal to 2, the deck can be partitioned into equal groups. Otherwise, forming valid groups is impossible.

X of a Kind in a Deck of Cards Python or Java solution

Python and Java implementations both follow the same idea: build a frequency map, then compute the GCD across all counts. Python typically uses collections.Counter and math.gcd, while Java uses HashMap with a helper GCD function. Both achieve O(n) time complexity.

What is the best approach for X of a Kind in a Deck of Cards?

The most efficient approach is frequency counting combined with the Greatest Common Divisor (GCD). Count how many times each card appears, then compute the GCD across all frequencies. If the GCD is at least 2, the deck can be split into groups of that size. This runs in O(n) time and O(n) space.

What data structure is used in X of a Kind in a Deck of Cards?

A hash table (hash map) is used to count how many times each card value appears. After building the frequency map, number theory operations like GCD are applied to those counts to determine whether a common group size exists.

What is the time complexity of X of a Kind in a Deck of Cards?

The optimal solution runs in O(n) time where n is the number of cards. One pass builds a frequency map, and another pass computes the GCD across counts. Space complexity is O(n) in the worst case when all cards are different.

Is X of a Kind in a Deck of Cards asked at Google, Amazon, or Meta?

This problem represents a typical interview pattern involving counting and number theory. Variants of frequency grouping and GCD checks have appeared in interviews at companies like Amazon and Google, especially for screening rounds focused on hash maps and mathematical reasoning.

Description Solution Video 15:48

914. X of a Kind in a Deck of Cards

Easy30.4% acceptance2 companies

You are given an integer array deck where deck[i] represents the number written on the i^th card.

Partition the cards into one or more groups such that:

Each group has exactly x cards where x > 1, and
All the cards in one group have the same integer written on them.

Return true if such partition is possible, or false otherwise.

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.

Constraints:

1 <= deck.length <= 10⁴
0 <= deck[i] < 10⁴

Asked at 2 companies

Google Amazon

Topics

15:48

Still stuck?Read 3 approaches, or watch a walkthrough.

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1class Solution:
2    def hasGroupsSizeX(self, deck: List[int]) -> bool:
3        

Starter codePython 3Spaces: 4

Examples

Case 1Case 2

Input

[1,2,3,4,4,3,2,1]

Input

[1,1,1,2,2,2,3,3]

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