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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

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.

 1 class Solution {
 2     func arraysIntersection(_ arr1: [Int], _ arr2: [Int], _ arr3: [Int]) -> [Int] {
 3         var m:[Int:Int] = [Int:Int]()
 4         for a in arr1 {m[a,default:0] += 1}
 5         for a in arr2 {m[a,default:0] += 1}
 6         for a in arr3 {m[a,default:0] += 1}
 7         var res:[Int] = [Int]()
 8         for (key,val) in m
 9         {
10             if val == 3
11             {
12                 res.append(key)
13             }
14         }
15         return res.sorted(by:<)
16     }
17 }