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

**Example 1:**

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

**Example 2:**

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

**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?