Topological Sorting

Given a directed graph, find a topological order of the graph.

Valid Number

Given a string, validate that it is a valid number.

Simplify Path

Given an absolute path for a file (Unix-style), simplify it.

Longest Consecutive Sequence

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

Sort List

Sort a linked list in O(n log n) time using constant space complexity.

Linked List Cycle II

Given a linked list, return the node where the cycle begins.

Interleaving String

Given three strings: s1, s2, s3, determine whether s3 is formed by the interleaving of s1 and s2.

Print Numbers by Recursion

Print numbers from 1 to the largest number with n digits by recursion.

Remove Duplicates from Sorted List II

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

Letter Combinations of a Phone Number

Given a string of digits, excluding 0 and 1, return all possible letter combinations that the number could represent.