diff --git a/longest-substring-without-repeating-characters/moonjonghoo.js b/longest-substring-without-repeating-characters/moonjonghoo.js
new file mode 100644
index 000000000..c777da2a4
--- /dev/null
+++ b/longest-substring-without-repeating-characters/moonjonghoo.js
@@ -0,0 +1,20 @@
+/**
+ * @param {string} s
+ * @return {number}
+ */
+const lengthOfLongestSubstring = function (s) {
+  let longest = 0;
+  let start = 0;
+  const seen = {};
+
+  for (let i = 0; i < s.length; i++) {
+    const char = s[i];
+    if (seen[char] >= start) {
+      start = seen[char] + 1;
+    }
+    seen[char] = i;
+    longest = Math.max(longest, i - start + 1);
+  }
+
+  return longest;
+};
diff --git a/number-of-islands/moonjonghoo.js b/number-of-islands/moonjonghoo.js
new file mode 100644
index 000000000..e69de29bb
diff --git a/reverse-linked-list/moonjonghoo.js b/reverse-linked-list/moonjonghoo.js
new file mode 100644
index 000000000..452a032e0
--- /dev/null
+++ b/reverse-linked-list/moonjonghoo.js
@@ -0,0 +1,13 @@
+var reverseList = function (head) {
+  let prev = null;
+  let current = head;
+
+  while (current !== null) {
+    let nextTemp = current.next; // 1. 다음 노드 기억해둠
+    current.next = prev; // 2. 포인터 방향 뒤집기
+    prev = current; // 3. prev 이동
+    current = nextTemp; // 4. current 이동
+  }
+
+  return prev; // prev가 새로운 head
+};