LeetCode 1213. 三个有序数组的交集（哈希set）

示例：
输入: arr1 = [1,2,3,4,5], arr2 = [1,2,5,7,9], arr3 = [1,3,4,5,8]
输出: [1,5]
解释: 只有 1 和 5 同时在这三个数组中出现.
 
提示：
1 <= arr1.length, arr2.length, arr3.length <= 1000
1 <= arr1[i], arr2[i], arr3[i] <= 2000

class Solution {
public:
    vector<int> arraysIntersection(vector<int>& arr1, vector<int>& arr2, vector<int>& arr3) {
    	unordered_set<int> s2(arr2.begin(), arr2.end()), s3(arr3.begin(),arr3.end());
    	vector<int> ans;
    	for(int i = 0; i < arr1.size(); ++i)
    	{
    		if(s2.find(arr1[i]) != s2.end() 
    				&& s3.find(arr1[i])!=s3.end())
    			ans.push_back(arr1[i]);
    	}
    	return ans;
    }
};