# 2. Classical Questions

- [Maximum Depth of Binary Tree](/algo/binary-tree/2.-classical-questions/maximum-depth-of-binary-tree.md): ID: 104; easy
- [Average of Levels in Binary Tree](/algo/binary-tree/2.-classical-questions/average-of-levels-in-binary-tree.md): ID: 1115; easy; 二叉树每层的平均数
- [Binary Tree Leaf Sum](/algo/binary-tree/2.-classical-questions/binary-tree-leaf-sum.md): ID: 481; easy; 二叉树叶子节点之和
- [Invert Binary Tree](/algo/binary-tree/2.-classical-questions/invert-binary-tree.md): ID: 226; easy
- [Binary Tree Path Sum](/algo/binary-tree/2.-classical-questions/binary-tree-path-sum.md): ID: 376; easy;  二叉树的路径和
- [Binary Tree Path Sum II](/algo/binary-tree/2.-classical-questions/binary-tree-path-sum-ii.md): ID: 246; medium; 二叉树的路径和 II
- [Binary Tree Path Sum III](/algo/binary-tree/2.-classical-questions/binary-tree-path-sum-iii.md): ID: 472; hard; 二叉树的路径和 III
- [Clone Binary Tree](/algo/binary-tree/2.-classical-questions/clone-binary-tree.md): ID: 375; medium; 克隆二叉树
- [Sum Root to Leaf Numbers](/algo/binary-tree/2.-classical-questions/sum-root-to-leaf-numbers.md): ID: 1353; medium; 根节点到叶节点求和
- [Binary Tree Level Sum](/algo/binary-tree/2.-classical-questions/binary-tree-level-sum.md): ID: 482; easy; 二叉树的某层节点之和
- [Binary Tree Paths](/algo/binary-tree/2.-classical-questions/binary-tree-paths.md): ID: 257; easy