94. Binary Tree Inorder Traversal

Given the root of a binary tree, return the inorder traversal of its nodes’ values.

Example 1:

1 2	Input: root = [1,null,2,3] Output: [1,3,2]

Example 2:

1 2	Input: root = [] Output: []

Example 3:

1 2	Input: root = [1] Output: [1]

Example 4:

1 2	Input: root = [1,2] Output: [2,1]

Example 5:

1 2	Input: root = [1,null,2] Output: [1,2]

二元樹尋訪應該是樹類最基本題目了，尋訪分三種，前序，中序，後序，依照值(root.val)位置決定是哪種。

1
2
3

preorder: 中->左->右  
inorder: 左->中->右  
postorder: 左->右->中

而題目需要中序，所以可以寫成

def inOrder(root): 
    if root != None: 
        inOrder(root.left)  
        print(root.val,end=" ")  
        inOrder(root.right)

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