Robina Li

This page covers specialized algorithmic techniques that appear in Hard-level LeetCode problems and competitive programming. These are not everyday patterns — most interviews won’t require them — but when a...

LeetCode Categories and Solution Templates

Given a binary array bits that ends with 0, determine whether the last character must be a 1-bit character.

Reverse the array of characters s in-place using O(1) extra memory.

Difficulty: Medium Category: Linked List, Circular List Companies: Amazon, Facebook, Google, Microsoft

Difficulty: Medium Category: Stack, Parsing, Simulation Companies: Amazon, Facebook, Google, Twitter

Difficulty: Medium Category: Tree, DFS, BFS Companies: Amazon, Facebook, Google, Microsoft, Apple

Difficulty: Medium Category: String, Stack Companies: Amazon, Facebook, Microsoft, Google

Difficulty: Medium Category: Array, Sorting, Simulation Companies: Amazon, Google, Microsoft, Uber

Difficulty: Medium Category: Tree, Linked List, DFS Companies: Amazon, Microsoft, Facebook