1. ​​112. Path Sum （重要）​​

2. ​​113. Path Sum II​​

3.​​129. Sum Root to Leaf Numbers​​

4.  

124. Binary Tree Maximum Path Sum（难）

5. ​​编程之美: 求二叉树中节点的最大距离​​

6. 

236. Lowest Common Ancestor of a Binary Tree