Inorder traversal (Left -> Root -> Right) can be implemented recursively or iteratively using a stack.

1. Initialize an empty result list.
2. Define a helper function traverse(node):
   • If node is None, return.
   • traverse(node.left)
   • result.append(node.val)
   • traverse(node.right)
3. Call traverse(root).
4. Return result.

• Time Complexity: O(N), where N is the number of nodes.
• Space Complexity: O(H), where H is the height of the tree (recursion stack).

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def inorder_traversal(root):
    res = []
    def helper(node):
        if not node:
            return
        helper(node.left)
        res.append(node.val)
        helper(node.right)
        
    helper(root)
    return res