349. Intersection of Two Arrays

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.

求两个集合的交集  结果元素必须唯一

C++（6ms）：

class Solution {
public:
    vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
        unordered_set<int> s(nums1.begin(),nums1.end()) ;
        vector<int> ans ;
        for (int i = 0; i < nums2.size();i++ ){
           if(s.count(nums2[i])){
              ans.push_back(nums2[i]) ;
              s.erase(nums2[i]);
           }
        }
        return ans;
    }
};

java(5ms):

class Solution {
    public int[] intersection(int[] nums1, int[] nums2) {
        Set<Integer> set = new HashSet<>() ;
        for(int i = 0 ; i < nums1.length ; i++){
            set.add(nums1[i]) ;
        }
        List<Integer> list = new ArrayList<>() ;        
        for(int i : nums2){
            if (set.contains(i)){
                list.add(i) ;
                set.remove(i) ;
            }
        }
        int[] res = new int[list.size()] ;
        for(int i = 0  ; i < list.size() ; i++){
            res[i] = list.get(i) ;
        }
        return res ;
    }
}