Commit db302c4

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Binary Tree Traversal

Inorder Recursive, Inorder Iterative, Preorder Recursive, Preorder Iterative, PostOrder Recursive, PostOrder Iterative, Level-Order Traversals

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`@@ -44,6 +44,26 @@ def inorder_traversal_recur(self, root):`
`44`	`44`	`self.inorder_traversal_recur(root.right)`
`45`	`45`	`else:`
`46`	`46`	`return`
	`47`	`+`
	`48`	`+ def inorderTraversalIterative(self, root: TreeNode) -> List[int]:`
	`49`	`+ """`
	`50`	`+ We need to use a Data Structure which gives us recently visited nodes thus, we use STACK(LIFO). There can be a time when stack`
	`51`	`+ is empty but we haven't visited the whole tree/ all the nodes so we iterate until the stack is empty or node!=None.`
	`52`	`+ If node is None it means left or right leaf is reached and we need to trace back to recently visited node's parent which isn't`
	`53`	`+ yet visited or whose right or left leaves are still unvisited. Keep adding them to the stack and popping them if node is None.`
	`54`	`+ """`
	`55`	`+ stack = list()`
	`56`	`+ inorder_traversal = list()`
	`57`	`+ node = root`
	`58`	`+ while node or len(stack):`
	`59`	`+ if node:`
	`60`	`+ stack.append(node)`
	`61`	`+ node = node.left`
	`62`	`+ else:`
	`63`	`+ node = stack.pop()`
	`64`	`+ inorder_traversal.append(node.val)`
	`65`	`+ node = node.right`
	`66`	`+ return inorder_traversal`
`47`	`67`
`48`	`68`
`49`	`69`

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