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?

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1 public class Solution { 2     public int[] intersect(int[] nums1, int[] nums2) { 3         Set
      
        set = new HashSet
       
        (); 4         Arrays.sort(nums1); 5         Arrays.sort(nums2); 6         for(int i = 0,j = 0; i < nums1.length && j < nums2.length;){ 7             if(nums1[i] == nums2[j]){ 8                 set.add(i++); 9                 j++;10             }else if(nums1[i] < nums2[j]) i++;11             else j++;12         }13         14         int[] ans = new int[set.size()];15         int k = 0;16         for(Integer n : set){17             ans[k++] = nums1[n];18         }19         return ans;20     }21 }
       
      

使用hashset 记录重复出现元素的下标。