Given the head of a singly linked list, return true if it is a palindrome.

Merge two sorted linked lists and return it as a sorted list. The list should be made by splicing together the nodes of the first two lists.

Given the head of a linked list and an integer val, remove all the nodes of the linked list that has Node.val == val, and return the new head.

Given the head of a singly linked list, reverse the list, and return the reversed list.

Given a string s consisting only of letters ‘a’ and ‘b’. In a single step you can remove one palindromic subsequence from s.

Design a HashMap without using any built-in hash table libraries.

Given a non-empty binary tree, return the average value of the nodes on each level in the form of an array.

Implement strStr().

Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Write a program to find the node at which the intersection of two singly linked lists begins.

Given an array nums and a value val, remove all instances of that value in-place and return the new length.