Given two arrays, write a function to compute their intersection.
Example:
Given nums1 = [1, 2, 2, 1], nums2 = [2, 2], return [2].
Note:
- Each element in the result must be unique.
- The result can be in any order.
https://discuss.leetcode.com/topic/45685/three-java-solutions
** 解题思路**
三种解法：
Use two hash sets , O(n) Time complexity
先把nums1加入到set中，然后用nums2中元素在set中遍历，如果set包含该元素，就加入到intersect set中。最后把intersect set 存入结果数组。Sort both arrays, use two pointers O(nlogn) Time complexity
Binary search O(nlogn) Time complexity
先sort nums2 ，然后用nums1元素在nums2中做binary search。如果能找到，就加入结果集。
