Leetcode binary tree inorder traversal

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+# Binary tree
+
++ [Binary Tree Inorder Traversal (iterative, threaded)](#binary-tree-inorder-traversal-iterative-threaded)
++ [Binary Tree Inorder Traversal (recursive)](#binary-tree-inorder-traversal-recursive)
++ [Binary Tree Inorder Traversal (iterative, stack)](#binary-tree-inorder-traversal-iterative-stack)
+
+## Binary Tree Inorder Traversal (iterative, threaded)
+
+https://leetcode.com/problems/binary-tree-inorder-traversal/
+
+```python
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution(object):
+    def inorderTraversal(self, root):
+        """
+        :type root: TreeNode
+        :rtype: List[int]
+        """
+        head = root
+        inorderlist = []
+        while head:
+            if not head.left:
+                inorderlist.append(head.val)
+                head = head.right
+            elif head.left:
+                curNode = head.left
+                while head.left and curNode.right and curNode.right != head:
+                    curNode = curNode.right
+                if not curNode.right:
+                    curNode.right = head
+                    head = head.left
+                elif curNode.right == head:
+                    inorderlist.append(head.val)
+                    curNode.right = None
+                    head = head.right
+        return inorderlist
+
+```
+
+## Binary Tree Inorder Traversal (recursive)
+
+https://leetcode.com/problems/binary-tree-inorder-traversal/
+
+```python
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution(object):
+    def inorderTraversal(self, root):
+        """
+        :type root: TreeNode
+        :rtype: List[int]
+        """
+        head = root
+        return self.inorderTraversal(head.left) + [head.val] + self.inorderTraversal(head.right) if head else []
+
+```
+
+## Binary Tree Inorder Traversal (iterative, stack)
+
+https://leetcode.com/problems/binary-tree-inorder-traversal/
+
+```python
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution(object):
+    def inorderTraversal(self, root):
+        """
+        :type root: TreeNode
+        :rtype: List[int]
+        """
+        if not root:
+            return []
+        stack = []
+        inorderlist = []
+        while stack or root:
+            if root:
+                stack.append(root)
+                root = root.left
+            else:
+                node = stack.pop()
+                inorderlist.append(node.val)
+                root = node.right
+        return inorderlist
+
+```