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

Example:
Given nums1 = [1, 2, 2, 1], nums2 = [2, 2], return [2, 2].

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? 


import collections
class Solution(object):
    def intersect(self, nums1, nums2):
        """
        :type nums1: List[int]
        :type nums2: List[int]
        :rtype: List[int]
        """
        c1 = collections.Counter(nums1)
        c2 = collections.Counter(nums2)
        ans = []
        (key1, key2) = (c1,c2) if len(c1)<len(c2) else (c2,c1)
        for k in key1:
            if k in key2:
                values = min(key1[k],key2[k])
                [ans.append(k) for _ in range(values)]
        return ans