Is Divide Array Into Equal Pairs easy or hard?

Divide Array Into Equal Pairs is categorized as an Easy problem on LeetCode with a high acceptance rate. The core idea is recognizing that every number must appear an even number of times, which can be verified with a simple frequency count.

Divide Array Into Equal Pairs Python/Java solution

In Python, use a dictionary or collections.Counter to track frequencies and check if each count is even. In Java, a HashMap performs the same role. Both implementations follow the same O(n) counting strategy.

How to solve Divide Array Into Equal Pairs in O(n)?

Traverse the array and store counts of each number in a hash map. After counting, check that every frequency is divisible by two. If any count is odd, return false; otherwise return true. Hash table operations keep the overall complexity at O(n).

What is the best approach for Divide Array Into Equal Pairs?

The best approach uses a hash map to count the frequency of each number. Iterate through the array, record how many times each value appears, and verify that every frequency is even. This method runs in O(n) time with O(n) extra space and works for any unsorted array.

Is Divide Array Into Equal Pairs asked at Google/Amazon/Meta?

Problems involving frequency counting and pair validation commonly appear in interviews at companies like Amazon, Google, and Meta. This problem specifically tests hash table usage, counting logic, and reasoning about element parity in arrays.

What data structure is used in Divide Array Into Equal Pairs?

A hash table (or dictionary) is typically used to store element frequencies. It allows constant-time insertion and lookup while counting occurrences, which enables the optimal O(n) solution.

What is the time complexity of Divide Array Into Equal Pairs?

The optimal solution runs in O(n) time using a frequency count with a hash table. Each element is processed once while updating counts. A sorting-based alternative requires O(n log n) time because of the sort operation.

Description Hints 2 Solution Video 6:48

2206. Divide Array Into Equal Pairs

Easy79.2% acceptance5 companies

You are given an integer array nums consisting of 2 * n integers.

You need to divide nums into n pairs such that:

Each element belongs to exactly one pair.
The elements present in a pair are equal.

Return true if nums can be divided into n pairs, otherwise return false.

Example 1:

Input: nums = [3,2,3,2,2,2]
Output: true
Explanation: 
There are 6 elements in nums, so they should be divided into 6 / 2 = 3 pairs.
If nums is divided into the pairs (2, 2), (3, 3), and (2, 2), it will satisfy all the conditions.

Example 2:

Input: nums = [1,2,3,4]
Output: false
Explanation: 
There is no way to divide nums into 4 / 2 = 2 pairs such that the pairs satisfy every condition.

Constraints:

nums.length == 2 * n
1 <= n <= 500
1 <= nums[i] <= 500

Asked at 5 companies

Microsoft Bloomberg

Google Amazon Meta

Topics

Hints open one at a time

Hint 1

For any number x in the range [1, 500], count the number of elements in nums whose values are equal to x.

Hint 2

The elements with equal value can be divided completely into pairs if and only if their count is even.

6:48

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