diff --git a/contains-duplicate/sonjh1217.swift b/contains-duplicate/sonjh1217.swift
new file mode 100644
index 0000000000..1ad3ae4fd2
--- /dev/null
+++ b/contains-duplicate/sonjh1217.swift
@@ -0,0 +1,14 @@
+class Solution {
+    // time O(n) / space O(n)
+    func containsDuplicate(_ nums: [Int]) -> Bool {
+        var numSet = Set<Int>()
+        for num in nums {
+            if numSet.contains(num) {
+                return true
+            }
+            numSet.insert(num)
+        }
+
+        return false
+    }
+}
diff --git a/two-sum/sonjh1217.swift b/two-sum/sonjh1217.swift
new file mode 100644
index 0000000000..ebbf8c5216
--- /dev/null
+++ b/two-sum/sonjh1217.swift
@@ -0,0 +1,15 @@
+class Solution {
+    // time O(n) / space O(n)
+    func twoSum(_ nums: [Int], _ target: Int) -> [Int] {
+        var indicesByCounters = [Int: Int]()
+        for (i, num) in nums.enumerated() { 
+            if let index = indicesByCounters[num] {
+                return [index, i]
+            }
+
+            indicesByCounters[target - num] = i
+        }
+
+        return []
+    }
+}