diff --git a/contains-duplicate/leebeanbin.java b/contains-duplicate/leebeanbin.java
new file mode 100644
index 000000000..0ccaabd01
--- /dev/null
+++ b/contains-duplicate/leebeanbin.java
@@ -0,0 +1,18 @@
+import java.util.HashSet;
+
+class Solution {
+	public boolean containsDuplicate(int[] nums) {
+		HashSet<Integer> arr = new HashSet<Integer>();
+		boolean answer = false;
+
+		for(int num : nums){
+			arr.add(num);
+		}
+
+		if(nums.length != arr.size()){
+			answer = true;
+		}
+
+		return answer;
+	}
+}
diff --git a/top-k-frequent-elements/leebeanbin.java b/top-k-frequent-elements/leebeanbin.java
new file mode 100644
index 000000000..caddcc468
--- /dev/null
+++ b/top-k-frequent-elements/leebeanbin.java
@@ -0,0 +1,16 @@
+import java.util.HashMap;
+import java.util.Map;
+
+public class Solution {
+	public int[] topKFrequent(int[] nums, int k) {
+		Map<Integer, Integer> map = new HashMap<>();
+
+		// count how many duplicated numbers in the input array
+		for (int num : nums) {
+			map.put(num, map.getOrDefault(num, 0) + 1);
+		}
+
+		return map.entrySet().stream().sorted((a, b) -> b.getValue() - a.getValue()).limit(k)
+				.mapToInt(Map.Entry::getKey).toArray();
+	}
+}
diff --git a/two-sum/leebeanbin.java b/two-sum/leebeanbin.java
new file mode 100644
index 000000000..0070edcc4
--- /dev/null
+++ b/two-sum/leebeanbin.java
@@ -0,0 +1,28 @@
+import java.util.HashMap;
+
+public class leebeanbin {
+	public static int[] bruteForce(int[] nums, int target) {
+		for (int i = 0; i < nums.length; i++) {
+			for (int j = i + 1; j < nums.length; j++) {
+				if (nums[i] + nums[j] == target) {
+					return new int[]{i, j};
+				}
+			}
+		}
+		return null;
+	}
+
+	public static int[] hashMap(int[] nums, int target) {
+		HashMap<Integer, Integer> arr = new HashMap<>();
+
+		for (int i = 0; i < nums.length; i++) {
+			arr.put(nums[i], i);
+
+			if (arr.containsKey(target - nums[i])) {
+				return new int[]{arr.get(target - nums[i]), i};
+			}
+		}
+
+		return null;
+	}
+}