diff --git a/contains-duplicate/dohee789.java b/contains-duplicate/dohee789.java
new file mode 100644
index 000000000..7c9e8cc9c
--- /dev/null
+++ b/contains-duplicate/dohee789.java
@@ -0,0 +1,17 @@
+/*
+https://leetcode.com/problems/contains-duplicate/
+ */
+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/house-robber/dohee789.java b/house-robber/dohee789.java
new file mode 100644
index 000000000..c820e003a
--- /dev/null
+++ b/house-robber/dohee789.java
@@ -0,0 +1,21 @@
+/*
+https://leetcode.com/problems/house-robber/
+ */
+class Solution{
+    public int rob(int[] nums){
+        if(nums.length == 0 || nums == null) return 0;
+        if(nums.length == 1) return 0;
+
+        int prev1 = 0;
+        int prev2 = 0;
+        for(int num: nums){
+            int temp = Math.max(prev1, prev2+num);
+            prev2 = prev1;
+            prev1 = temp;
+        }
+
+        return prev1;
+    }
+}
+
+
diff --git a/longest-consecutive-sequence/dohee789.java b/longest-consecutive-sequence/dohee789.java
new file mode 100644
index 000000000..eaf7ce6d9
--- /dev/null
+++ b/longest-consecutive-sequence/dohee789.java
@@ -0,0 +1,26 @@
+/*
+https://leetcode.com/problems/longest-consecutive-sequence/
+ */
+class Solution {
+    public int longestConsecutive(int[] nums) {
+        Set<Integer> set = new HashSet<>();
+        for(int num: nums){
+            set.add(num);
+        }
+
+        int maxLength = 0;
+        for(int num: set){
+            if(!set.contains(num-1)){
+                int currentNum = num;
+                int length = 1;
+                while(set.contains(currentNum+1)){
+                    currentNum++;
+                    length++;
+                }
+                maxLength = Math.max(maxLength,length);
+            }
+        }
+        return maxLength;
+    }
+}
+
diff --git a/top-k-frequent-elements/dohee789.java b/top-k-frequent-elements/dohee789.java
new file mode 100644
index 000000000..9de7f1974
--- /dev/null
+++ b/top-k-frequent-elements/dohee789.java
@@ -0,0 +1,31 @@
+/*
+https://leetcode.com/problems/top-k-frequent-elements/
+ */
+class Solution {
+    public int[] topKFrequent(int[] nums, int k) {
+        Map<Integer, Integer> freqMap = new HashMap<>();
+        for(int num: nums){
+            freqMap.put(num, freqMap.getOrDefault(num,0)+1);
+        }
+
+        PriorityQueue<Map.Entry<Integer, Integer>> minHeap = new PriorityQueue<>(
+                Comparator.comparingInt(Map.Entry::getValue)
+        );
+
+        for (Map.Entry<Integer, Integer> entry : freqMap.entrySet()) {
+            minHeap.offer(entry);
+            if (minHeap.size() > k) {
+                minHeap.poll();
+            }
+        }
+
+        int[] result = new int[k];
+        for (int i = 0; i < k; i++) {
+            result[i] = minHeap.poll().getKey();
+        }
+
+        return result;
+
+    }
+}
+
diff --git a/two-sum/dohee789.java b/two-sum/dohee789.java
new file mode 100644
index 000000000..08afb456a
--- /dev/null
+++ b/two-sum/dohee789.java
@@ -0,0 +1,19 @@
+/*
+https://leetcode.com/problems/two-sum/
+ */
+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        Map<Integer, Integer> map = new HashMap<>();
+
+        for(int i = 0; i < nums.length; i++) {
+            if(map.containsKey(target - nums[i])) {
+                int j = map.get(target - nums[i]);
+                return new int[]{j, i};
+            }
+            map.put(nums[i], i);
+        }
+
+        return null;
+    }
+}
+