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0144_binaryTreePreorderTraversal.py
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0144_binaryTreePreorderTraversal.py
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# 0144 - Binary Tree Postorder Traversal
'''
Question:
Given the root of a binary tree, return the preorder traversal of its nodes' values.
'''
# 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 preorderTraversal(self, root):
"""
:type root: TreeNode
:rtype: List[int]
"""
# Solution 1 - Recursive
ans = []
if root is None:
return ans
self.preorder(root, ans)
return ans
def preorder(self, node, ans):
if node:
ans.append(node.val)
if node.left:
self.preorder(node.left, ans)
if node.right:
self.preorder(node.right, ans)
# # Solution 2 - Iterative
# if root is None:
# return []
# stack, ans = [root], []
# while stack:
# node = stack.pop()
# ans.append(node.val)
# if node.right:
# stack.append(node.right)
# if node.left:
# stack.append(node.left)
# return ans
if __name__ == '__main__':
root = TreeNode(val = 1, right = TreeNode(val = 2, right=TreeNode(val = 3)))
# root = TreeNode(val = 1)
sol = Solution()
print(sol.preorderTraversal(root))