Tree traversal - Preorder

tree_traversal_preorder.py

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

def preorder_traversal_recursive(root):
    result = []

    def recur(node):
        # base case
        if not node:
            return

        # visit node
        result.append(node.val)
        # traverse the left subtree
        recur(node.left)
        # traverse the right subtree
        recur(node.right)

    recur(root)
    return result