## Representing Graph and Tree

Representing a graph or tree by a matrix or adjacent node lists.

Representing a graph or tree by a matrix or adjacent node lists.

Given a binary tree, find its maximum depth.

Given a binary tree, find its minimum depth.

Given a binary tree, return the level order traversal of its nodes' values.

Given a binary tree, return the bottom-up level order traversal of its nodes' values.

Help the robot to find all the unique paths from (0,0) to (m,n) with obstacles

Given a 2D board and a word, find if the word exists in the grid.