Intersection of Two Arrays II Problem

Question

Given two arrays, write a function to compute their intersection.

Example 1:

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

Example 2:

Input: nums1 = [4,9,5], nums2 = [9,4,9,8,4]
Output: [4,9]

Note:

• Each element in the result should appear as many times as it shows in both arrays.
• The result can be in any order.

Follow up:

• What if the given array is already sorted? How would you optimize your algorithm?
• What if nums1's size is small compared to nums2's size? Which algorithm is better?
• What if elements of nums2 are stored on disk, and the memory is limited such that you cannot load all elements into the memory at once?

Answer 1

Simple count all the occurance of each number for nums 1 and then compare its freq from nums 2 to get final ans.

class Solution:     def intersect(self, nums1: List[int], nums2: List[int]) -> List[int]:         dict1 = dict()         for i in nums1:             if i not in dict1:                 dict1[i] = 1             else:                 dict1[i] += 1         ret = []         for i in nums2:             if i in dict1 and dict1[i]>0:                 ret.append(i)                 dict1[i] -= 1         return ret

eg : ans = Solution()

nums1 = [1,2,2,1], nums2 = [2,2]

ans.intersect(nums1, nums2)

Output -

[2,2]