diff --git a/contains-duplicate/s0ooo0k.java b/contains-duplicate/s0ooo0k.java
new file mode 100644
index 000000000..5b0dd8c37
--- /dev/null
+++ b/contains-duplicate/s0ooo0k.java
@@ -0,0 +1,19 @@
+/*
+ * 시간복잡도 O(n)
+ * 공간복잡도 O(n)
+ */
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        Set<Integer> set = new HashSet<>();
+
+        for(int n : nums) {
+            if(set.contains(n)){
+                return true;
+            }
+            set.add(n);
+        }
+        return false;
+    }
+}
+
+
diff --git a/two-sum/s0ooo0k.java b/two-sum/s0ooo0k.java
new file mode 100644
index 000000000..6e393fc53
--- /dev/null
+++ b/two-sum/s0ooo0k.java
@@ -0,0 +1,48 @@
+import java.util.Map;
+
+class Solution {
+
+    /*
+     * 시간복잡ㄷ도 개선
+     * 
+     * 시간복잡도 O(n)
+     * 공간복잡도 O(n)
+     */
+    public int[] twoSum(int[] nums, int target) {
+        Map<Integer, Integer> arr = new HashMap<>();
+
+        for(int i=0; i<nums.length; i++) {
+            if(arr.containsKey(target-nums[i])) {
+                return new int[]{arr.get(target-nums[i]), i};
+            }
+            arr.put(nums[i], i);
+        }
+        return new int[]{0, 0};
+    }
+    
+    
+    
+    /*
+     * 기존 풀이
+     * 
+     * 시간복잡도 O(n^2)
+     * 공간복잡도 O(1)
+     */
+
+    /*
+    public int[] twoSum(int[] nums, int target) {
+        int[] answer = new int[2];
+        for(int i=0; i<nums.length; i++) {
+            for(int j=i+1; j<nums.length; j++) {
+                if(nums[i]+nums[j]==target) {
+                    answer[0]=i;
+                    answer[1]=j;
+                    return answer;
+                }
+            }
+        }
+        return answer;
+    }
+    */
+}
+