2206. Divide Array Into Equal Pairs

Description

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

Solutions

Solution: Hash Map

Time complexity: O(n)
Space complexity: O(n)

JavaScript

js

/**
 * @param {number[]} nums
 * @return {boolean}
 */
const divideArray = function (nums) {
  const countMap = new Map();

  for (const num of nums) {
    const count = countMap.get(num) ?? 0;

    countMap.set(num, count + 1);
  }

  for (const count of countMap.values()) {
    if (count % 2) return false;
  }

  return true;
};