diff --git a/contains-duplicate/shinheekim.java b/contains-duplicate/shinheekim.java
new file mode 100644
index 000000000..500e67260
--- /dev/null
+++ b/contains-duplicate/shinheekim.java
@@ -0,0 +1,15 @@
+import java.util.HashSet;
+import java.util.Set;
+
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        Set<Integer> visited = new HashSet<>();
+
+        for (int n : nums){
+            if (!visited.add(n)){
+                return true;
+            }
+        }
+        return false; // 모든 값이 고유할 때
+    }
+}
diff --git a/two-sum/shinheekim.java b/two-sum/shinheekim.java
new file mode 100644
index 000000000..fc37d6fb6
--- /dev/null
+++ b/two-sum/shinheekim.java
@@ -0,0 +1,16 @@
+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        int[] result = 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){
+                    result[0] = i;
+                    result[1] = j;
+                    return result;
+                }
+            }
+        }
+        return null;
+    }
+}