diff --git a/contains-duplicate/hancrysta1.java b/contains-duplicate/hancrysta1.java
new file mode 100644
index 000000000..9a9e3cfc6
--- /dev/null
+++ b/contains-duplicate/hancrysta1.java
@@ -0,0 +1,8 @@
+import java.util.*;
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        Set<Integer> numSet = Arrays.stream(nums).boxed().collect(Collectors.toSet());
+        if(numSet.size()!=nums.length) return true;
+        else return false;
+    }
+}
diff --git a/top-k-frequent-elements/hancrysta1.java b/top-k-frequent-elements/hancrysta1.java
new file mode 100644
index 000000000..dab94ffa5
--- /dev/null
+++ b/top-k-frequent-elements/hancrysta1.java
@@ -0,0 +1,17 @@
+import java.util.*;
+class Solution {
+    public int[] topKFrequent(int[] nums, int k) {
+        Map<Integer,Integer> count = new HashMap<>();
+        for(int i=0;i<nums.length;i++){
+            count.put(nums[i],count.getOrDefault(nums[i],0)+1);
+        }
+        List<Integer> sortedCount = new ArrayList<>(count.keySet());
+        sortedCount.sort((a,b)->count.get(b)-count.get(a));//value 기준 키 정렬
+        int[] answer = new int[k];
+        for(int i=0;i<k;i++){
+            answer[i] = sortedCount.get(i);
+        }
+        
+        return answer;
+    }
+}
diff --git a/valid-palindrome/hancrysta1.java b/valid-palindrome/hancrysta1.java
new file mode 100644
index 000000000..627b4aa76
--- /dev/null
+++ b/valid-palindrome/hancrysta1.java
@@ -0,0 +1,18 @@
+import java.util.*;
+class Solution {
+    public boolean isPalindrome(String s) {
+        String words = s.toLowerCase().replaceAll("[^0-9A-Za-z]","");
+        //System.out.println(words);
+        Deque<Character> stack = new ArrayDeque<>();
+        for(int i=0;i<words.length();i++){
+            stack.push(words.charAt(i));
+        }
+        while(!stack.isEmpty()){
+            for(int i=0;i<words.length();i++){
+                if(words.charAt(i)==stack.pop()) continue;
+                else return false;
+            }
+        }
+        return true;
+    }
+}