Binary preamble, in sequence, after traversal (Python)

prologue:

 1 class Solution:
 2     def preorderTraversal(self, root: TreeNode) -> List[int]:
 3         res=[]
 4         stack=[]
 5         while root or stack:
 6             if root:
 7                 stack.append(root)
 8                 res.append(root.val)
 9                 root=root.left
10             else:
11                 root=stack.pop()
12                 root=root.right
13         return res

After the sequence:

 1 class Solution:
 2     def postorderTraversal(self, root: TreeNode) -> List[int]:
 3         stack=[]
 4         res=[]
 5         while root or stack:
 6             if root:
 7                 stack.append(root)
 8                 res.append(root.val)
 9                 root=root.right
10             else:
11                 root=stack.pop()
12                 root=root.left
13         return res[::-1]

In order:

 1 class Solution:
 2     def inorderTraversal(self, root: TreeNode) -> List[int]:
 3         stack=[]
 4         res=[]
 5         while stack or root:
 6             if root:
 7                 stack.append(root)
 8                 root=root.left
 9             else:
10                 root = stack.pop()
11                 res.append(root.val)
12                 root=root.right
13         return res

2019-12-27 21:56:55