Problem

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

Pre analysis

Will keep a track of number of occurences of number and then check if all numbers are even.

Another solution

/**
 * @param {number[]} nums
 * @return {boolean}
 */
var canBePaired = function (nums) {
  let map = {};
  for (let i = 0; i < nums.length; i++) {
    map[nums[i]] = (map[nums[i]] || 0) + 1;
  }
  for (let key in map) {
    if (map[key] % 2 !== 0) {
      return false;
    }
  }
  return true;
};

/**
 * @param {number[]} nums
 * @return {boolean}
 */
var divideArray = function (nums) {
  const numMap = new Map();
  for (const num of nums) {
    numMap.has(num) ? numMap.delete(num) : numMap.set(num, true);
  }
  return numMap.size === 0;
};