diff --git a/contains-duplicate/dalpang81.java b/contains-duplicate/dalpang81.java
new file mode 100644
index 000000000..2a8269ab3
--- /dev/null
+++ b/contains-duplicate/dalpang81.java
@@ -0,0 +1,11 @@
+//시간복잡도 : O(nlogn)
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        Arrays.sort(nums);
+        for(int i = 0; i < nums.length - 1; i++) {
+            if(nums[i] == nums[i+1])
+                return true;
+        }
+        return false;
+    }
+}
diff --git a/house-robber/dalpang81.java b/house-robber/dalpang81.java
new file mode 100644
index 000000000..e5f76b68a
--- /dev/null
+++ b/house-robber/dalpang81.java
@@ -0,0 +1,19 @@
+//시간복잡도 O(n)
+class Solution {
+    public int rob(int[] nums) {
+        if (nums.length == 1) {
+            return nums[0];
+        }
+
+        int temp2 = nums[0];
+        int temp1 = Math.max(nums[0], nums[1]);
+
+        for (int i = 2; i < nums.length; i++) {
+            int current = Math.max(temp1, nums[i] + temp2);
+            temp2 = temp1;
+            temp1 = current;
+        }
+
+        return temp1;
+    }
+}
diff --git a/longest-consecutive-sequence/dalpang81.java b/longest-consecutive-sequence/dalpang81.java
new file mode 100644
index 000000000..d5cfa414f
--- /dev/null
+++ b/longest-consecutive-sequence/dalpang81.java
@@ -0,0 +1,33 @@
+//시간복잡도: O(n)
+import java.util.*;
+
+class Solution {
+    public int longestConsecutive(int[] nums) {
+        Set<Integer> numSet = new HashSet<>();
+        for (int num : nums) {
+            numSet.add(num);
+        }
+
+        int longNum = 0;
+
+        // 각 숫자에 대해 시퀀스 시작 여부를 확인
+        for (int num : numSet) {
+            // num-1이 없는 경우에만 시퀀스를 시작
+            if (!numSet.contains(num - 1)) {
+                int currentNum = num;
+                int currentLong = 1;
+
+                // 연속된 숫자를 탐색
+                while (numSet.contains(currentNum + 1)) {
+                    currentNum++;
+                    currentLong++;
+                }
+
+                // 가장 긴 시퀀스를 갱신
+                longNum = Math.max(longNum, currentLong);
+            }
+        }
+
+        return longNum;
+    }
+}
diff --git a/top-k-frequent-elements/dalpang81.java b/top-k-frequent-elements/dalpang81.java
new file mode 100644
index 000000000..569869398
--- /dev/null
+++ b/top-k-frequent-elements/dalpang81.java
@@ -0,0 +1,31 @@
+//시간복잡도: O(n + mlogk)
+import java.util.*;
+class Solution {
+    public int[] topKFrequent(int[] nums, int k) {
+        Map<Integer, Integer> map = new HashMap<>();
+
+
+        for(int i : nums) {
+            map.put(i, map.getOrDefault(i,0) + 1);
+        }
+
+        PriorityQueue<Map.Entry<Integer, Integer>> pq =
+                new PriorityQueue<>(Comparator.comparingInt(Map.Entry::getValue));
+
+        for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
+            pq.offer(entry);
+            if (pq.size() > k) {
+                pq.poll(); // Remove the least frequent element
+            }
+        }
+
+        // Step 3: Extract the elements from the heap
+        int[] result = new int[k];
+        for (int i = k - 1; i >= 0; i--) {
+            result[i] = pq.poll().getKey();
+        }
+
+        return result;
+
+    }
+}
diff --git a/valid-palindrome/dalpang81.java b/valid-palindrome/dalpang81.java
new file mode 100644
index 000000000..c2ef2bbea
--- /dev/null
+++ b/valid-palindrome/dalpang81.java
@@ -0,0 +1,13 @@
+//시간복잡도: O(n)
+class Solution {
+    public boolean isPalindrome(String s) {
+        s = s.toLowerCase().trim();
+        s = s.replaceAll("[^a-z0-9]", "");
+
+        StringBuffer sb = new StringBuffer(s);
+        String reverse = sb.reverse().toString();
+
+        return(s.equals(reverse));
+
+    }
+}