2206. Divide Array Into Equal Pairs

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.

class Solution {
public:
    bool divideArray(vector<int>& nums) {
        int n = nums.size();
        if(n & 1) return false;
        unordered_set<int> s;
        for(int n : nums) {
            if(s.count(n)) s.erase(n);
            else s.insert(n);
        }
        return s.size() == 0;
    }
};