2215. Find the Difference of Two Arrays

1. Description

Given two 0-indexed integer arrays nums1 and nums2, return a list answer of size 2 where:

• answer[0] is a list of all distinct integers in nums1 which are not present in nums2.
• answer[1] is a list of all distinct integers in nums2 which are not present in nums1.

Note that the integers in the lists may be returned in any order.

2. Example

Example 1:
Input: nums1 = [1,2,3], nums2 = [2,4,6]
Output: [[1,3],[4,6]]
Explanation:
For nums1, nums1[1] = 2 is present at index 0 of nums2, whereas nums1[0] = 1 and nums1[2] = 3 are not present in nums2. Therefore, answer[0] = [1,3].
For nums2, nums2[0] = 2 is present at index 1 of nums1, whereas nums2[1] = 4 and nums2[2] = 6 are not present in nums1. Therefore, answer[1] = [4,6].

Example 2:
Input: nums1 = [1,2,3,3], nums2 = [1,1,2,2]
Output: [[3],[]]
Explanation:
For nums1, nums1[2] and nums1[3] are not present in nums2. Since nums1[2] == nums1[3], their value is only included once and answer[0] = [3].
Every integer in nums2 is present in nums1. Therefore, answer[1] = [].

3. Constraints

• 1 <= nums1.length, nums2.length <= 1000
• -1000 <= nums1[i], nums2[i] <= 1000

4. Solutions

Hash Table

n = nums1.size() + nums2.size()
Time complexity: O(n)
Space complexity: O(n)

class Solution {
public:
    vector<vector<int>> findDifference(const vector<int> &nums1, const vector<int> &nums2) {
        unordered_set<int> unique_nums1, unique_nums2;
        for (auto num : nums1) {
            unique_nums1.insert(num);
        }
        for (auto num : nums2) {
            unique_nums2.insert(num);
        }

        vector<vector<int>> differences(2);
        for (int num : unique_nums1) {
            if (unique_nums2.find(num) == unique_nums2.end()) {
                differences[0].push_back(num);
            }
        }
        for (int num : unique_nums2) {
            if (unique_nums1.find(num) == unique_nums1.end()) {
                differences[1].push_back(num);
            }
        }
        return differences;
    }
};