binary-tree-preorder-traversal.py

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def preorderTraversal(self, root):
        if not root:
            return []

        stack = [root]
        result = []

        while stack:
            node = stack.pop()

            result.append(node.val)

            if node.right:
                stack.append(node.right)

            if node.left:
                stack.append(node.left)

        return result