Intersection of Three Sorted Arrays

Given three integer arrays arr1, arr2 and arr3 sorted in strictly increasing order, return a sorted array of only the integers that appeared in all three arrays.

 

Example 1:

Input: arr1 = [1,2,3,4,5], arr2 = [1,2,5,7,9], arr3 = [1,3,4,5,8] Output: [1,5] Explanation: Only 1 and 5 appeared in the three arrays.

 

Constraints:

• 1 <= arr1.length, arr2.length, arr3.length <= 1000

• 1 <= arr1[i], arr2[i], arr3[i] <= 2000

** USE HASH MAP

class Solution {
public:
    vector arraysIntersection(vector& arr1, vector& arr2, vector& arr3) {
        map<int, int> hmap;
        for(int i = 0; i < arr1.size(); i++)
        {
            hmap[arr1.at(i)] = 1;
        }
        for(int i = 0; i < arr2.size(); i++)
        {
            int each = arr2.at(i);
            if(hmap.find(each) != hmap.end())
            {
                hmap[each]++;
            }
        }
        for(int i = 0; i < arr3.size(); i++)
        {
            int each = arr3.at(i);
            if(hmap.find(each) != hmap.end())
            {
                hmap[each]++;
            }
        }
        vector res;
        map<int, int>::iterator iter;
        for(iter = hmap.begin(); iter != hmap.end(); iter++)
        {
            if(iter->second == 3)
            {
                res.push_back(iter->first);
            }
        }
        return res;
    }
};