Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

Given the root of a binary tree, then value v and depth d, you need to add a row of nodes with value v at the given depth d. The root node is at depth 1.

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.

A valid encoding of an array of words is any reference string s and array of indices indices such that:

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.

Given an array nums containing n distinct numbers in the range [0, n], return the only number in the range that is missing from the array.