Divide Array Into Equal Pairs

Just create a map, count, to maintain the count of every num in nums. Then, when interating through nums, just xor count[num] with 1 and then increment / decrement unpaired_count depending on if count[num] is equal to 1 or 0.

Finally, if unpaired_count > 0, then we know nums cannot be divided into n pairs.

code

class Solution {
public:
    bool divideArray(vector<int>& nums) {
        int count[501] = {0};
        int unpaired_count = 0;
        for (int num : nums) {
            count[num] ^= 1;
            if (count[num]) {
                ++unpaired_count;
            } else {
                --unpaired_count;
            }
        }
        return (unpaired_count) ? false : true;
    }
};

complexity

• Time: O(n)
• Space: O(n)

time taken

• that took me less than a minute I swear