Find the Difference of Two Arrays

Published: Feb 9, 2023

Easy Array

Problem 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.

Constraints:

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

https://leetcode.com/problems/find-the-difference-of-two-arrays/

Examples

Example 1
Input: nums1 = [1,2,3], nums2 = [2,4,6]
Output: [[1,3],[4,6]]

Example 2
Input: nums1 = [1,2,3,3], nums2 = [1,1,2,2]
Output: [[3],[]]

How to Solve

Nothing is complicated in this problem. Start from creating two sets from given two arrays since those arrays have duplicates. The next step depends on the language. Python has a feature to get sets difference by just a ‘-‘ (minus) operator. Other languages don’t have such handy feature, so easy way would be iterate the set one by one while checking the presence of values in another set. If the value is not present in another set, add it to the result array.

Solution

class FindTheDifferenceOfTwoArrays {
public:
    vector<vector<int>> findDifference(vector<int>& nums1, vector<int>& nums2) {
        unordered_set<int> s1(nums1.begin(), nums1.end()), s2(nums2.begin(), nums2.end());
        vector<vector<int>> result(2, vector<int>{});
        for (auto v : s1) {
            if (s2.find(v) == s2.end()) { result[0].push_back(v); }
        }
        for (auto v : s2) {
            if (s1.find(v) == s1.end()) { result[1].push_back(v); }
        }
        return result;
    }
};



**
 * @param {number[]} nums1
 * @param {number[]} nums2
 * @return {number[][]}
 */
var findDifference = function(nums1, nums2) {
  let s1 = new Set(nums1), s2 = new Set(nums2);
  let result = [[], []];
  s1.forEach(v => {
    if (!s2.has(v)) { result[0].push(v); }
  })
  s2.forEach(v => {
    if (!s1.has(v)) { result[1].push(v); }
  })
  return result;
};

class FindTheDifferenceOfTwoArrays:
    def findDifference(self, nums1: List[int], nums2: List[int]) -> List[List[int]]:
        s1, s2 = set(nums1), set(nums2)
        return [list(s1 - s2), list(s2 -s1)]

Complexities

  • Time: O(n)
  • Space: O(n)