LeetCode 75 — TypeScript

Parallel companion to leetcode-75-go and leetcode-75-py. One folder per problem grouped under category folders.

Setup

npm install

Run

# Single problem
npx vitest run 02-two-pointers/01-move-zeroes

# One category
npx vitest run 02-two-pointers

# Everything
npm test

Stubs use it.skip(...) so unimplemented problems don't break the suite. Switch it.skip to it in solution.test.ts once you start a problem.

Layout

<category>/<NN>-<kebab-slug>/
  solution.ts        // standalone function stub, returns zero value
  solution.test.ts   // it.skip + scratch space for cases

Numbering is per-category (01..N within each topic), not global across all 75. The category folder gives you the topic; the number gives you the recommended order within the topic.

Tree / linked-list problems include the TreeNode / ListNode class at the top of solution.ts — matches how LeetCode pre-fills the editor.

Each solution.ts is a standalone ES module (export function ...). The companion solution.test.ts imports from ./solution.

Progress (75 problems)

Array / String

• 01 Merge Strings Alternately (1768)
• 02 Greatest Common Divisor of Strings (1071)
• 03 Kids With the Greatest Number of Candies (1431)
• 04 Can Place Flowers (605)
• 05 Reverse Vowels of a String (345)
• 06 Reverse Words in a String (151)
• 07 Product of Array Except Self (238)
• 08 Increasing Triplet Subsequence (334)
• 09 String Compression (443)

Two Pointers

• 01 Move Zeroes (283)
• 02 Is Subsequence (392)
• 03 Container With Most Water (11)
• 04 Max Number of K-Sum Pairs (1679)

Sliding Window

• 01 Maximum Average Subarray I (643)
• 02 Maximum Number of Vowels in a Substring of Given Length (1456)
• 03 Max Consecutive Ones III (1004)
• 04 Longest Subarray of 1's After Deleting One Element (1493)

Prefix Sum

• 01 Find the Highest Altitude (1732)
• 02 Find Pivot Index (724)

Hash Map / Set

• 01 Find the Difference of Two Arrays (2215)
• 02 Unique Number of Occurrences (1207)
• 03 Determine if Two Strings Are Close (1657)
• 04 Equal Row and Column Pairs (2352)

Stack

• 01 Removing Stars From a String (2390)
• 02 Asteroid Collision (735)
• 03 Decode String (394)

Queue

• 01 Number of Recent Calls (933)
• 02 Dota2 Senate (649)

Linked List

• 01 Delete the Middle Node of a Linked List (2095)
• 02 Odd Even Linked List (328)
• 03 Reverse Linked List (206)
• 04 Maximum Twin Sum of a Linked List (2130)

Binary Tree - DFS

• 01 Maximum Depth of Binary Tree (104)
• 02 Leaf-Similar Trees (872)
• 03 Count Good Nodes in Binary Tree (1448)
• 04 Path Sum III (437)
• 05 Longest ZigZag Path in a Binary Tree (1372)
• 06 Lowest Common Ancestor of a Binary Tree (236)

Binary Tree - BFS

• 01 Binary Tree Right Side View (199)
• 02 Maximum Level Sum of a Binary Tree (1161)

Binary Search Tree

• 01 Search in a Binary Search Tree (700)
• 02 Delete Node in a BST (450)

Graphs - DFS

• 01 Keys and Rooms (841)
• 02 Number of Provinces (547)
• 03 Reorder Routes to Make All Paths Lead to the City Zero (1466)
• 04 Evaluate Division (399)

Graphs - BFS

• 01 Nearest Exit from Entrance in Maze (1926)
• 02 Rotting Oranges (994)

Heap / Priority Queue

• 01 Kth Largest Element in an Array (215)
• 02 Smallest Number in Infinite Set (2336)
• 03 Maximum Subsequence Score (2542)
• 04 Total Cost to Hire K Workers (2462)

Binary Search

• 01 Guess Number Higher or Lower (374)
• 02 Successful Pairs of Spells and Potions (2300)
• 03 Find Peak Element (162)
• 04 Koko Eating Bananas (875)

Backtracking

• 01 Letter Combinations of a Phone Number (17)
• 02 Combination Sum III (216)

DP - 1D

• 01 N-th Tribonacci Number (1137)
• 02 Min Cost Climbing Stairs (746)
• 03 House Robber (198)
• 04 Domino and Tromino Tiling (790)

DP - Multidimensional

• 01 Unique Paths (62)
• 02 Longest Common Subsequence (1143)
• 03 Best Time to Buy and Sell Stock with Transaction Fee (714)
• 04 Edit Distance (72)

Bit Manipulation

• 01 Counting Bits (338)
• 02 Single Number (136)
• 03 Minimum Flips to Make a OR b Equal to c (1318)

Trie

• 01 Implement Trie (Prefix Tree) (208)
• 02 Search Suggestions System (1268)

Intervals

• 01 Non-overlapping Intervals (435)
• 02 Minimum Number of Arrows to Burst Balloons (452)

Monotonic Stack

• 01 Daily Temperatures (739)
• 02 Online Stock Span (901)

TypeScript idioms worth front-loading

• Arrays have .push / .pop (stack), .shift / .unshift (slow at the front — O(n)); reach for an index pointer or a deque for queues
• No built-in heap — write a small MinHeap<T> class with siftUp/siftDown, or negate values for max-heap
• Map preserves insertion order and accepts any key type; plain objects coerce keys to strings
• Set for membership tests; new Set(arr1).intersection(new Set(arr2)) (ES2025) — older Node: filter
• Strings are immutable; build with array.join(""), not += in a loop
• Array.from({ length: n }, (_, i) => ...) to build/initialize; new Array(n).fill(0) for plain fills
• arr.sort((a, b) => a - b) — the default comparator is lexicographic; always pass a numeric comparator for numbers
• 2D arrays: Array.from({ length: m }, () => new Array(n).fill(0)) — avoid fill(new Array(...)) (shared reference)
• for (const [i, x] of arr.entries()) for index + value
• Tuple destructuring: [a, b] = [b, a + b]