Medium level algorithm and data structure challenges.

Add Two Numbers**Challenge:** You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.**Topics Covered:** Linked List

Binary Tree Inorder Traversal**Challenge:** Given a binary tree, return the *inorder* traversal of its nodesâ€™ values.**Topics Covered:** Recursion, Tree

Container With Most Water**Challenge:** Given array of pylon heights, find max area of water in between.**Topics Covered:** Array, Two Pointer

Merge Intervals**Challenge:** Given a collection of intervals, merge all overlapping intervals.**Topics Covered:** Array, Sort

Odd Even Linked List**Challenge:** Given a binary tree, determine if it is a valid binary search tree (BST).**Topics Covered:** Linked List

Product of Array Except Self**Challenge:** Given an array nums of n integers where n > 1, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].**Topics Covered:** Array, Dynamic Programming

Remove Nth Node From End of List**Challenge:** Given a linked list, remove the n-th node from the end of list and return its head.**Topics Covered:** Linked List

Subsets**Challenge:** Given a set of distinct integers, nums, return all possible subsets (the power set).**Topics Covered:** Array

Top K Frequent Elements**Challenge:** Given a non-empty array of integers, return the ** k** most frequent elements.

**Topics Covered:**Hash Table, Array, Sort

Trapping Rain Water**Challenge:** Given *n* non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining.**Topics Covered:** Array, Dynamic Programming

Unique Paths**Challenge:** How many possible unique paths are there?**Topics Covered:** Array, Dynamic Programming

Validate Binary Search Tree**Challenge:** Given a binary tree, determine if it is a valid binary search tree (BST).**Topics Covered:** Binary Tree, DFS