[Swift]LeetCode1213. 三个有序数组的交集 | Intersection of Three Sorted Arrays

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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

---

给出三个均为 严格递增排列 的整数数组 arr1，arr2 和 arr3。

返回一个由 仅 在这三个数组中 同时出现 的整数所构成的有序数组。 

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. 1 <= arr1.length, arr2.length, arr3.length <= 1000
2. 1 <= arr1[i], arr2[i], arr3[i] <= 2000

---

Runtime: 84 ms

Memory Usage: 21.5 MB

class Solution {
    func arraysIntersection(_ arr1: [Int], _ arr2: [Int], _ arr3: [Int]) -> [Int] {
        var m:[Int:Int] = [Int:Int]()
        for a in arr1 {m[a,default:0] += 1}
        for a in arr2 {m[a,default:0] += 1}
        for a in arr3 {m[a,default:0] += 1}
        var res:[Int] = [Int]()
        for (key,val) in m
        {
            if val == 3
            {
                res.append(key)
            }
        }
        return res.sorted(by:<)
    }
}