[Array] Refactor solution to Intersection of Two Arrays

Author: soapyigu

Array/IntersectionTwoArrays.swift

@@ -1,13 +1,23 @@
 /**
  * Question Link: https://leetcode.com/problems/intersection-of-two-arrays/
- * Primary idea: Use set interact function to help
+ * Primary idea: Use set to hold numbers for one array and iterate the other one to output result, 
+ *               remove the number from set to avoid duplicates.
+ *
+ * Note: Do not use built-in intersection function for Set in Swift, that is not this question is asking for.
  *
  * Time Complexity: O(n), Space Complexity: O(n)
  *
  */
 
 class IntersectionTwoArrays {
-    func intersection(nums1: [Int], _ nums2: [Int]) -> [Int] {
-        return Array(Set(nums1).intersection(Set(nums2)))
+    func intersection(_ nums1: [Int], _ nums2: [Int]) -> [Int] { 
+        var set = Set(nums1), res = [Int]()
+        
+        for num in nums2 where set.contains(num) {
+            res.append(num)
+            set.remove(num)
+        }
+        
+        return res
     }
 }