Robina Li

Given a reference of a node in a connected undirected graph.

You have a lock in front of you with 4 circular wheels. Each wheel has 10 slots: '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'. The wheels can...

Given the root of a binary tree, return the vertical order traversal of its nodes’ values. (i.e., from top to bottom, column by column).

You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money.

Difficulty: Medium Category: Backtracking, Recursion, Duplicates

Given two integers n and k, return all possible combinations of k numbers chosen from the range [1, n].

Difficulty: Medium Category: Backtracking, Recursion

Difficulty: Medium Category: Tree, Binary Tree, LCA

Difficulty: Medium Category: Design, Data Structure

Difficulty: Medium Category: Tree, DFS, BFS, Graph