input: Write a python function to return all root-to-leaf paths in a binary tree as a list of strings.
  assert traverseTree(TreeNode(1)) == ['1']
  root = TreeNode(1)
  root.left = TreeNode(2)
  root.right = TreeNode(3)
  assert traverseTree(root) == ['12', '13']
  root.left.left = TreeNode(4)
  root.left.right = TreeNode(5)
  assert traverseTree(root) == ['124', '125', '13']
output: class TreeNode:
      def __init__(self, val=0, left=None, right=None):
          self.val = val
          self.left = left
          self.right = right
  
  def traverseTree(root):
      if not root:
          return []
  
      def dfs(node, path, paths):
          if not node.left and not node.right:
              paths.append(path)
          if node.left:
              dfs(node.left, path + str(node.left.val), paths)
          if node.right:
              dfs(node.right, path + str(node.right.val), paths)
  
      paths = []
      dfs(root, str(root.val), paths)
      return paths