Leetcode Intersection of Two Arrays problem solution

from collections import Counter
class Solution:
    def intersection(self, nums1: List[int], nums2: List[int]) -> List[int]:
        d1, d2 = Counter(nums1), Counter(nums2)
        out = []
        for i in d1.keys():
            if i in d2.keys():
                out.append(i)
        return out

public int[] intersection(int[] nums1, int[] nums2) {
        HashSet<Integer> set = new HashSet<>();
        ArrayList<Integer> intersection = new ArrayList<>();
        
        for (int i = 0; i < nums1.length; i++) {
            set.add(nums1[i]);
        }
        
        for (int i = 0; i < nums2.length; i++) {
            if (set.remove(nums2[i])) {
                intersection.add(nums2[i]);
            }
        }
        
        int[] result = new int[intersection.size()];
        for (int i = 0; i < intersection.size(); i++) {
            result[i] = intersection.get(i);
        }
        
        return result;
    }

class Solution {
public:
    vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
        int i = 0 , j = 0 , prev = -1;
        sort(nums1.begin() , nums1.end());
        sort(nums2.begin() , nums2.end());
        vector<int>ans;
        while(i<nums1.size() && j<nums2.size()){
            if(nums1[i] == nums2[j]){
                if(prev == -1 || prev != nums1[i]){
                    ans.push_back(nums1[i]);
                    prev = nums1[i];
                }
                i++;
                j++;
            }
            else if(nums1[i] > nums2[j]){
                j++;
            }
            else if(nums1[i] < nums2[j]){
                i++;
            }
        }
        return ans;
    }
};

int* intersection(int* nums1, int nums1Size, int* nums2, int nums2Size, int* returnSize){
    
    int i, j = 0;
    int size = nums1Size < nums2Size ? nums1Size : nums2Size;
    int hash [1000] = {0};
    int *res = (int *) malloc(size*sizeof(int));
    
    for (i = 0; i < nums1Size; i++)
        hash[nums1[i]] = 1;

    for (i = 0; i< nums2Size; i++) {
        if (hash[nums2[i]] == 1) {
            res[j++] = nums2[i];
            hash[nums2[i]] = 2;
        }
    }
    
    *returnSize = j;
    
    return res;
}