leetcode-116 - Populating Next Right Pointers in Each Node
動機 畫裡面那一個橢圓，很有趣 ...
Tree
leetcode-114 - Flatten Binary Tree to Linked List
動機 preorder的tree threading ...
leetcode-199 - Binary Tree Right Side View
動機 複習bfs ...
leetcode-96 - Unique Binary Search Trees
動機 當成range，就可以去二分了 ...
leetcode-337 - House Robber III
動機 樹型dp 用sum(list of list,[])去攤平一層 ...
leetcode-437 - Path Sum III
動機 原來是prefix sum的靈壓!! ...
leetcode-236 - Lowest Common Ancestor of a Binary Tree
動機 我忘了localty ...
leetcode-94 - Binary Tree Inorder Traversal
動機 中序的英文是inorder，一開始寫以為是前序 ...
leetcode-101 - Symmetric Tree
動機 複習bfs ...
leetcode-235 - Lowest Common Ancestor of a Binary Search Tree
動機 善用binary search tree，所以才是easy ...