350. Intersection of Two Arrays II java solutions

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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public class Solution {
    public int[] intersect(int[] nums1, int[] nums2) {
        Set<Integer> set = new HashSet<Integer>();
        Arrays.sort(nums1);
        Arrays.sort(nums2);
        for(int i = 0,j = 0; i < nums1.length && j < nums2.length;){
            if(nums1[i] == nums2[j]){
                set.add(i++);
                j++;
            }else if(nums1[i] < nums2[j]) i++;
            else j++;
        }
        
        int[] ans = new int[set.size()];
        int k = 0;
        for(Integer n : set){
            ans[k++] = nums1[n];
        }
        return ans;
    }
}

使用hashset 记录重复出现元素的下标。