Write a program to reverse a singly linked list? Modify that program to reverse a doubly linked list.

Write a string to find a substring in a given string. Do this in O(n) or better

Write a function that takes as input two numbers represented as strings, and returns the product of the numbers of a string.

The numbers can be arbitrarily large.

Write a function that takes a an array of integers, and returns the contiguous subsequence of integers with the largest sum.