diff --git a/clone-graph/moonjonghoo.js b/clone-graph/moonjonghoo.js
new file mode 100644
index 000000000..32edc5670
--- /dev/null
+++ b/clone-graph/moonjonghoo.js
@@ -0,0 +1,36 @@
+/**
+ * // Definition for a Node.
+ * function Node(val, neighbors) {
+ *    this.val = val === undefined ? 0 : val;
+ *    this.neighbors = neighbors === undefined ? [] : neighbors;
+ * };
+ */
+
+/**
+ * @param {Node} node
+ * @return {Node}
+ */
+var cloneGraph = function (node) {
+  if (!node) return null;
+
+  const visited = new Map();
+
+  const dfs = (currNode) => {
+    if (visited.has(currNode)) {
+      return visited.get(currNode);
+    }
+
+    // 노드 복사
+    const clone = new Node(currNode.val);
+    visited.set(currNode, clone);
+
+    // 이웃 노드들도 복사해서 연결
+    for (let neighbor of currNode.neighbors) {
+      clone.neighbors.push(dfs(neighbor));
+    }
+
+    return clone;
+  };
+
+  return dfs(node);
+};
diff --git a/longest-common-subsequence/moonjonghoo.js b/longest-common-subsequence/moonjonghoo.js
new file mode 100644
index 000000000..e0deb203f
--- /dev/null
+++ b/longest-common-subsequence/moonjonghoo.js
@@ -0,0 +1,22 @@
+/**
+ * @param {string} text1
+ * @param {string} text2
+ * @return {number}
+ */
+var longestCommonSubsequence = function (text1, text2) {
+  const m = text1.length,
+    n = text2.length;
+  const dp = Array.from({ length: m + 1 }, () => Array(n + 1).fill(0));
+
+  for (let i = 1; i <= m; i++) {
+    for (let j = 1; j <= n; j++) {
+      if (text1[i - 1] === text2[j - 1]) {
+        dp[i][j] = dp[i - 1][j - 1] + 1;
+      } else {
+        dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
+      }
+    }
+  }
+
+  return dp[m][n];
+};
diff --git a/longest-repeating-character-replacement/moonjonghoo.js b/longest-repeating-character-replacement/moonjonghoo.js
new file mode 100644
index 000000000..09382f29b
--- /dev/null
+++ b/longest-repeating-character-replacement/moonjonghoo.js
@@ -0,0 +1,30 @@
+/**
+ * @param {string} s
+ * @param {number} k
+ * @return {number}
+ */
+var characterReplacement = function (s, k) {
+  let left = 0;
+  let maxCount = 0;
+  let freq = new Array(26).fill(0); // A~Z
+
+  let maxLength = 0;
+
+  for (let right = 0; right < s.length; right++) {
+    const idx = s.charCodeAt(right) - "A".charCodeAt(0);
+    freq[idx]++;
+    maxCount = Math.max(maxCount, freq[idx]);
+
+    let windowSize = right - left + 1;
+
+    if (windowSize - maxCount > k) {
+      const leftIdx = s.charCodeAt(left) - "A".charCodeAt(0);
+      freq[leftIdx]--;
+      left++;
+    }
+
+    maxLength = Math.max(maxLength, right - left + 1);
+  }
+
+  return maxLength;
+};
diff --git a/number-of-islands/moonjonghoo.js b/number-of-islands/moonjonghoo.js
index e69de29bb..cc06f35cc 100644
--- a/number-of-islands/moonjonghoo.js
+++ b/number-of-islands/moonjonghoo.js
@@ -0,0 +1,37 @@
+/**
+ * @param {character[][]} grid
+ * @return {number}
+ */
+const numIslands = function (grid) {
+  let count = 0;
+
+  const dfs = (i, j) => {
+    if (
+      i < 0 ||
+      i >= grid.length ||
+      j < 0 ||
+      j >= grid[i].length ||
+      grid[i][j] === "0"
+    ) {
+      return;
+    }
+
+    grid[i][j] = "0";
+
+    dfs(i + 1, j);
+    dfs(i - 1, j);
+    dfs(i, j + 1);
+    dfs(i, j - 1);
+  };
+
+  for (let i = 0; i < grid.length; i++) {
+    for (let j = 0; j < grid[i].length; j++) {
+      if (grid[i][j] === "1") {
+        dfs(i, j);
+        count++;
+      }
+    }
+  }
+
+  return count;
+};
diff --git a/palindromic-substrings/moonjonghoo.js b/palindromic-substrings/moonjonghoo.js
new file mode 100644
index 000000000..49c7fa13b
--- /dev/null
+++ b/palindromic-substrings/moonjonghoo.js
@@ -0,0 +1,22 @@
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var countSubstrings = function (s) {
+  let count = 0;
+
+  const expand = (left, right) => {
+    while (left >= 0 && right < s.length && s[left] === s[right]) {
+      count++;
+      left--;
+      right++;
+    }
+  };
+
+  for (let i = 0; i < s.length; i++) {
+    expand(i, i); // 홀수 길이 중심 (예: "aba")
+    expand(i, i + 1); // 짝수 길이 중심 (예: "aa")
+  }
+
+  return count;
+};
diff --git a/reverse-bits/moonjonghoo.js b/reverse-bits/moonjonghoo.js
new file mode 100644
index 000000000..d9590e381
--- /dev/null
+++ b/reverse-bits/moonjonghoo.js
@@ -0,0 +1,13 @@
+/**
+ * @param {number} n - a positive integer
+ * @return {number} - reversed bits
+ */
+var reverseBits = function (n) {
+  let result = 0;
+  for (let i = 0; i < 32; i++) {
+    result <<= 1; // 왼쪽으로 1비트 이동
+    result |= n & 1; // 마지막 비트 추출해서 결과에 추가
+    n >>>= 1; // 부호 없는 우측 시프트 (>>>)
+  }
+  return result >>> 0; // unsigned 32비트 정수로 변환
+};