From 8ae76f913d3b642293e2d365150df634a40d2443 Mon Sep 17 00:00:00 2001
From: danny <gryb809@gmail.com>
Date: Tue, 11 Aug 2026 16:09:49 +0900
Subject: [PATCH 1/3] 0190-reverse-bits

---
 reverse-bits/dahyeong-yun.java | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 reverse-bits/dahyeong-yun.java

diff --git a/reverse-bits/dahyeong-yun.java b/reverse-bits/dahyeong-yun.java
new file mode 100644
index 0000000000..1464849189
--- /dev/null
+++ b/reverse-bits/dahyeong-yun.java
@@ -0,0 +1,28 @@
+/**
+ * TC : O(1)
+ *   - 32번의 루프를 2번 반복하므로 O(1)
+ * SC : O(1)
+ *   - 32칸 고정 길이의 stack이 필요하므로 O(1)
+ */
+
+class Solution {
+    public int reverseBits(int n) {
+        int answer = 0;
+        Deque<Integer> stack = new ArrayDeque<>();
+
+        for(int i = 0; i<32; i++) {
+            stack.add(n % 2);
+            n /= 2;
+        }
+
+        int j = 0;
+        while(!stack.isEmpty()) {
+            int bit = stack.getLast();
+            stack.removeLast();
+            answer += bit * Math.pow(2, j); 
+            j += 1;
+        }
+
+        return answer;       
+    }
+}

From f2f234982748b6a6d6cd3e03ae211860129ac9f7 Mon Sep 17 00:00:00 2001
From: danny <gryb809@gmail.com>
Date: Fri, 14 Aug 2026 20:58:36 +0900
Subject: [PATCH 2/3] 0424-longest-repeating-character-replacement

---
 .../dahyeong-yun.java                         | 35 +++++++++++++++++++
 1 file changed, 35 insertions(+)
 create mode 100644 longest-repeating-character-replacement/dahyeong-yun.java

diff --git a/longest-repeating-character-replacement/dahyeong-yun.java b/longest-repeating-character-replacement/dahyeong-yun.java
new file mode 100644
index 0000000000..2fc0fab496
--- /dev/null
+++ b/longest-repeating-character-replacement/dahyeong-yun.java
@@ -0,0 +1,35 @@
+/**
+ * TC : O(n)
+ *   - 문자열의 길이 n 만큼 반복하고 루프 안에서는 고정 길이를 반복하므로 O(n)
+ * SC : O(1)
+ *   - 26개 알파벳의 카운트를 위한 배열을 생성하므로 O(1)
+ */
+class Solution {
+    public int characterReplacement(String s, int k) {
+        int max = 0;
+
+        int len = s.length();
+        int deleteTarget = 0;
+        int[] count = new int[26];
+        for(int i=0; i<len; i++) {
+            char c = s.charAt(i);
+            count[c - 'A']++;
+
+            
+            int maxCountAlphabet = 0;
+            int total = count[0];
+            for(int j=1; j<26; j++) {
+                total += count[j];    
+                if(count[j] > count[maxCountAlphabet]) maxCountAlphabet = j;
+            }
+
+            if(total - count[maxCountAlphabet] <= k) {
+                max = Math.max(max, total);
+            } else {
+                count[s.charAt(deleteTarget++) - 'A']--;
+            }
+        }
+
+        return max;
+    }
+}

From 9c89884c34ef0837ef38bda47008e8e3a8e7aacd Mon Sep 17 00:00:00 2001
From: danny <gryb809@gmail.com>
Date: Fri, 14 Aug 2026 21:53:44 +0900
Subject: [PATCH 3/3] 0647-palindromic-substrings

---
 palindromic-substrings/dahyeong-yun.java | 37 ++++++++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 palindromic-substrings/dahyeong-yun.java

diff --git a/palindromic-substrings/dahyeong-yun.java b/palindromic-substrings/dahyeong-yun.java
new file mode 100644
index 0000000000..c8e061ff98
--- /dev/null
+++ b/palindromic-substrings/dahyeong-yun.java
@@ -0,0 +1,37 @@
+/**
+ * TC : O(n^2)
+ *   - 문자열 길이 n 만큼 반복하고, 각 인덱스에서 n/2 만큼의 회문을 확인하므로 n * (n/2) => O(n^2)
+ * SC : O(1)
+ *   - 별도 유의미한 공간을 사용하지 않음 
+ */
+class Solution {
+    public int countSubstrings(String s) {
+        int len = s.length(), count = 0;
+
+        for(int i = 0; i<len; i++) {
+            int start = i, end = i;
+
+            // 홀수 길이 회문 카운트
+            while(
+                start >= 0 && end < len && s.charAt(start) == s.charAt(end)
+            ) {
+                count++;
+                start--;
+                end++;
+            }
+
+            // 짝수 길이 회문 카운트
+            start = i;
+            end = i+1;
+            while(
+                start >= 0 && end < len && s.charAt(start) == s.charAt(end)
+            ) {
+                count++;
+                start--;
+                end++;
+            }
+        }
+
+        return count;
+    }
+}