Intersection of Two Arrays

Level: Easy

Topics: Array, Hash Table, Two Pointers, Binary Search, Sorting

Given two integer arrays nums1 and nums2, return an array of their intersection. Each element in the result must be unique and you may return the result in any order.

Example 1:

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

Example 2:

Input: nums1 = [4,9,5], nums2 = [9,4,9,8,4]
Output: [9,4]
Explanation: [4,9] is also accepted.

Constraints:

• 1 <= nums1.length, nums2.length <= 1000

• 0 <= nums1[i], nums2[i] <= 1000

Approach:

Solution:

class Solution {
public:
    vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
        // Create unordered sets to store unique elements from nums1 and nums2
        unordered_set<int> set1(nums1.begin(), nums1.end());
        unordered_set<int> set2(nums2.begin(), nums2.end());

        //create a vector to store the intersection of set1 & set2
        vector<int> ans;

        // Iterate through each element in set1
        for(const auto &num : set1) {
            //check of current element from set1 exists in set2
            if(set2.find(num) != set2.end()) {
                //if the element exists in set2, add it to the intersection vector
                ans.push_back(num);
            }
        }
        //return the intersection vector
        return ans;
    }
};

Full Solution:

#include<iostream>
#include<unordered_set>
using namespace std;

vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
    unordered_set<int> set1(nums1.begin(), nums1.end());
    unordered_set<int> set2(nums2.begin(), nums2.end());

    vector<int> ans;
    for(const auto& num : set1) {
        if(set2.find(num) != set1.end()) {
            ans.push_back(num);
        }
    }
    return ans;
}

int main() {
    vector<int> nums1;
    nums1.push_back(1);
    nums1.push_back(2);
    nums1.push_back(2);
    nums1.push_back(1);

    vector<int> nums2;
    nums2.push_back(2);
    nums2.push_back(2);

    vector<int> ans = intersection(nums1, nums2);
    cout << "Output: ";
    for(int num : ans) {
        cout << num << " ";
    }
    cout << endl;
    return 0;
}