diff --git a/longest-substring-without-repeating-characters/taewanseoul.ts b/longest-substring-without-repeating-characters/taewanseoul.ts
new file mode 100644
index 000000000..3f3fc63e7
--- /dev/null
+++ b/longest-substring-without-repeating-characters/taewanseoul.ts
@@ -0,0 +1,31 @@
+/**
+ * 3. Longest Substring Without Repeating Characters
+ * Given a string s, find the length of the longest substring without repeating characters.
+ *
+ * https://leetcode.com/problems/longest-substring-without-repeating-characters/description/
+ *
+ */
+
+// O(n^2) time
+// O(n) space
+function lengthOfLongestSubstring(s: string): number {
+  let result = 0;
+
+  for (let i = 0; i < s.length; i++) {
+    let set = new Set();
+    let substring = 0;
+
+    for (let j = i; j < s.length; j++) {
+      if (set.has(s[j])) {
+        break;
+      }
+
+      set.add(s[j]);
+      substring++;
+    }
+
+    result = Math.max(result, substring);
+  }
+
+  return result;
+}
diff --git a/reverse-linked-list/taewanseoul.ts b/reverse-linked-list/taewanseoul.ts
new file mode 100644
index 000000000..ebc73a220
--- /dev/null
+++ b/reverse-linked-list/taewanseoul.ts
@@ -0,0 +1,45 @@
+/**
+ * 206. Reverse Linked List
+ * Given the head of a singly linked list, reverse the list, and return the reversed list.
+ *
+ * https://leetcode.com/problems/reverse-linked-list/description/
+ *
+ */
+
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+
+class ListNode {
+  val: number;
+  next: ListNode | null;
+  constructor(val?: number, next?: ListNode | null) {
+    this.val = val === undefined ? 0 : val;
+    this.next = next === undefined ? null : next;
+  }
+}
+
+// O(n) time
+// O(1) space
+function reverseList(head: ListNode | null): ListNode | null {
+  let prev: ListNode | null = null;
+  let next: ListNode | null = null;
+
+  while (head) {
+    next = head.next;
+    head.next = prev;
+
+    prev = head;
+    head = next;
+  }
+
+  return prev;
+}