Eulerian tour algorithm

eulerian_tour.py

# Eulerian tour algorithm https://en.wikipedia.org/wiki/Eulerian_path
def eulerian_tour(root: TreeNode) -> List[TreeNode]:
    tour = []
    def dfs(node: TreeNode, depth: int) -> None:
        tour.append((node.val, depth))
        if node.left:
            dfs(node.left, depth + 1)
            tour.append((node.val, depth))
        if node.right:
            dfs(node.right, depth + 1)
            tour.append((node.val, depth))
    dfs(root, 0)
    return tour