14. DFS Inorder

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Example 1:

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

Output: [1,3,2]

Explanation: The inorder traversal is: Left (null for node 1), Node (1), Right (node 2). Then for node 2: Left (3), Node (2), Right (null). Combined and flattened: [1, 3, 2]

Example 2:

Input: root = [1,2,3,4,5,null,8,null,null,6,7,9]

Output: [4,2,6,5,7,1,3,9,8]

Explanation: The inorder traversal is done recursively starting from the root. The order will be left subtree, current node, then right subtree

Example 3:

Input: root = []

Output: []

Explanation: An empty tree returns an empty list.

Example 4:

Input: root = [1]

Output: [1]

Explanation: A tree with a single node returns a list containing that node's value.

Constraints:

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Time Complexity

O(n)

Space Complexity

O(h)