Find Common Elements Between Two Arrays

Problem Description

You are given two integer arrays nums1 and nums2 of sizes n and m, respectively. Calculate the following values:

• answer1 : the number of indices i such that nums1[i] exists in nums2.
• answer2 : the number of indices i such that nums2[i] exists in nums1.

Return [answer1, answer2].

Key Insights

• We need to count how many elements from one array exist in the other array.
• Using a set can help in efficiently checking for existence of elements due to its average O(1) time complexity for lookups.
• The problem can be solved in linear time relative to the size of the input arrays.

Space and Time Complexity

Time Complexity: O(n + m), where n is the length of nums1 and m is the length of nums2.
Space Complexity: O(n + m) in the worst case for storing elements in sets.

Solution

To solve this problem, we will use two sets to store the unique elements from each array. We will then iterate through both arrays and count how many elements from each array exist in the other array using the sets.

1. Convert nums1 to a set for quick lookups.
2. Iterate through nums1 and check how many elements exist in nums2 using the set.
3. Repeat the process for nums2 with respect to nums1.
4. Return the counts as an array.

Code Solutions