diff --git a/longest-repeating-character-replacement/juhui-jeong.java b/longest-repeating-character-replacement/juhui-jeong.java
new file mode 100644
index 0000000000..2984b03a50
--- /dev/null
+++ b/longest-repeating-character-replacement/juhui-jeong.java
@@ -0,0 +1,26 @@
+/* 
+ * 시간복잡도: O(n)
+ * 공간복잡도: O(1)
+*/
+class Solution {
+    public int characterReplacement(String s, int k) {
+        int left = 0;
+        int[] freq = new int[26];
+        int maxFreq = 0;
+        int ans = 0;
+
+        for (int right = 0; right < s.length(); right++) {
+            int rIdx = s.charAt(right) - 'A';
+            freq[rIdx]++;
+            maxFreq = Math.max(maxFreq, freq[rIdx]);
+
+            while((right - left + 1) - maxFreq > k) {
+                int lIdx = s.charAt(left) - 'A';
+                freq[lIdx]--;
+                left++;
+            }
+            ans = Math.max(ans, right - left + 1);
+        }
+        return ans;
+    }
+}
diff --git a/reverse-bits/juhui-jeong.java b/reverse-bits/juhui-jeong.java
new file mode 100644
index 0000000000..3a8dd1cae8
--- /dev/null
+++ b/reverse-bits/juhui-jeong.java
@@ -0,0 +1,22 @@
+/*
+ * 시간 복잡도: O(1)
+ * 공간 복잡도: O(1)
+ */
+class Solution {
+
+    public static String toBinaryString(int value) {
+        String str = Integer.toBinaryString(value);
+        while (str.length() < 32) {
+            str = "0" + str;
+        }
+        return str;
+    }
+
+    public int reverseBits(int n) {
+        String binaryString = toBinaryString(n);
+        String reversed = new StringBuilder(binaryString).reverse().toString();
+        
+        int result = Integer.parseUnsignedInt(reversed, 2);
+        return result;
+    }
+}