diff --git a/contains-duplicate/jaekwang97.java b/contains-duplicate/jaekwang97.java
new file mode 100644
index 0000000000..08a28a54d7
--- /dev/null
+++ b/contains-duplicate/jaekwang97.java
@@ -0,0 +1,16 @@
+import java.util.*;
+
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        Set<Integer> seen = new HashSet<>();
+
+        for (int num : nums) {
+            if (seen.contains(num)) {
+                return true;
+            }
+            seen.add(num);
+        }
+
+        return false;
+    }
+}
diff --git a/top-k-frequent-elements/jaekwang97.java b/top-k-frequent-elements/jaekwang97.java
new file mode 100644
index 0000000000..d8ac29ff2e
--- /dev/null
+++ b/top-k-frequent-elements/jaekwang97.java
@@ -0,0 +1,38 @@
+import java.util.*;
+
+class Solution {
+    static class Item implements Comparable<Item> {
+        int num;
+        int count;
+
+        Item(int num, int count) {
+            this.num = num;
+            this.count = count;
+        }
+
+        @Override
+        public int compareTo(Item other) {
+            return Integer.compare(other.count, this.count);
+        }
+    }
+
+    public int[] topKFrequent(int[] nums, int k) {
+        Map<Integer, Integer> counts = new HashMap<>();
+
+        for (int num : nums) {
+            counts.put(num, counts.getOrDefault(num, 0) + 1);
+        }
+
+        PriorityQueue<Item> queue = new PriorityQueue<>();
+        for (Map.Entry<Integer, Integer> entry : counts.entrySet()) {
+            queue.add(new Item(entry.getKey(), entry.getValue()));
+        }
+
+        int[] answer = new int[k];
+        for (int i = 0; i < k; i++) {
+            answer[i] = queue.poll().num;
+        }
+
+        return answer;
+    }
+}
diff --git a/two-sum/jaekwang97.java b/two-sum/jaekwang97.java
new file mode 100644
index 0000000000..3ad4cf23a4
--- /dev/null
+++ b/two-sum/jaekwang97.java
@@ -0,0 +1,17 @@
+import java.util.*;
+
+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        Map<Integer, Integer> seen = new HashMap<>();
+
+        for (int i = 0; i < nums.length; i++) {
+            int complement = target - nums[i];
+            if (seen.containsKey(complement)) {
+                return new int[] { seen.get(complement), i };
+            }
+            seen.put(nums[i], i);
+        }
+
+        return new int[] {};
+    }
+}