## Path Sum

Given the root of a binary tree and an integer targetSum, return true if the tree has a root-to-leaf path such that adding up all the values along the path equals targetSum.

Given the root of a binary tree and an integer targetSum, return true if the tree has a root-to-leaf path such that adding up all the values along the path equals targetSum.

A robot is located at the top-left corner of a m x n grid (marked as ‘Start’ in the diagram below). The robot can either move right or diagonally at any point of time. The robot is trying to reach the top-right corner of the grid (marked as ‘Star’ in the diagram below). How many possible unique paths are there?

The robot is trying to move in a obstacle grid.

Find Unique Paths in a 2D Grid from Source to Destination

Given a string s, find the length of the longest substring t that contains at most 2 distinct characters.

Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right, which minimizes the sum of all numbers along its path.

Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.

Given a binary tree, return the vertical order traversal of its nodes’ values.

Given a binary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level).

Given a binary tree, you need to compute the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.