diff --git a/clone-graph/lhc0506.js b/clone-graph/lhc0506.js
new file mode 100644
index 000000000..2470e81a5
--- /dev/null
+++ b/clone-graph/lhc0506.js
@@ -0,0 +1,38 @@
+/**
+ * // 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 stack = [node];
+  const map = new Map();
+
+  map.set(node.val, new _Node(node.val));
+
+  while (stack.length > 0) {
+      const currentNode = stack.pop();
+
+      for (const neighbor of currentNode.neighbors) {
+          if (!map.has(neighbor.val)) {
+              map.set(neighbor.val, new Node(neighbor.val));
+              stack.push(neighbor);
+          }
+          map.get(currentNode.val).neighbors.push(map.get(neighbor.val));
+      }
+
+  }
+  return map.get(node.val);
+};
+
+
+// 시간복잡도: O(n)
+// 공간복잡도: O(n)
diff --git a/longest-repeating-character-replacement/lhc0506.js b/longest-repeating-character-replacement/lhc0506.js
new file mode 100644
index 000000000..5d1e899a1
--- /dev/null
+++ b/longest-repeating-character-replacement/lhc0506.js
@@ -0,0 +1,32 @@
+/**
+ * @param {string} s
+ * @param {number} k
+ * @return {number}
+ */
+var characterReplacement = function(s, k) {
+  let start = 0;
+  let maxFreq = 0;
+  let result = 0;
+  const map = new Map();
+
+  for (let end = 0; end < s.length; end++) {
+      const endChar = s[end];
+      map.set(endChar, 1 + (map.get(endChar) || 0));
+
+      maxFreq = Math.max(maxFreq, map.get(endChar));
+
+      if (end - start + 1 - maxFreq > k) {
+          const startChar = s[start];
+          map.set(startChar, map.get(startChar) - 1);
+          start++;
+
+      }
+
+      result = Math.max(result, end - start + 1);
+  }
+
+  return result;
+};
+
+// 시간복잡도: O(n)
+// 공간복잡도: O(1)
diff --git a/palindromic-substrings/lhc0506.js b/palindromic-substrings/lhc0506.js
new file mode 100644
index 000000000..c6fc56441
--- /dev/null
+++ b/palindromic-substrings/lhc0506.js
@@ -0,0 +1,30 @@
+/**
+ * @param {string} s
+ * @return {number}
+ */
+
+var countSubstrings = function(s) {
+  let count = 0;
+  for (let i = 0; i < s.length; i++) {
+      let start = i;
+      let end = i;
+      while (start >= 0 && end < s.length && s[start] === s[end]) {
+          count += 1;
+          start -= 1;
+          end += 1;
+      }
+
+      start = i;
+      end = i + 1;
+      while (start >= 0 && end < s.length && s[start] === s[end]) {
+          count += 1;
+          start -= 1;
+          end += 1;
+      }
+  }
+
+  return count;
+};
+
+// 시간 복잡도: O(n^2)
+// 공간 복잡도: O(1)
diff --git a/reverse-bits/lhc0506.js b/reverse-bits/lhc0506.js
new file mode 100644
index 000000000..ca9e5c793
--- /dev/null
+++ b/reverse-bits/lhc0506.js
@@ -0,0 +1,10 @@
+/**
+ * @param {number} n - a positive integer
+ * @return {number} - a positive integer
+ */
+var reverseBits = function(n) {
+  return parseInt(n.toString(2).padStart(32, '0').split('').reverse().join(''), 2);
+};
+
+// 시간복잡도: O(n)
+// 공간복잡도: O(1)