Program to traverse binary tree using list of directions in Python

Suppose we have a binary tree and a list of strings moves consisting of "R"(Right), "L"(Left) and "U"(Up). Starting from root, we have to traverse the tree by performing each move in moves where: "R" indicates traverse to the right child. "L" indicates traverse to the left child. "U" indicates traverse to its parent.

So, if the input is like

["R","R","U","L"], then the output will be 3

To solve this, we will follow these steps −

• past := a new list

• for each move in moves, do

  • insert root at the end of past

  • if move is same as "L", then

    • root := left of root

  • otherwise when move is same as "R", then

    • root := right of root

  • otherwise,

    • delete last element from past

    • root := last element from past and delete it from past

• return value of root

Let us see the following implementation to get better understanding −

Example

 Live Demo

class TreeNode:
   def __init__(self, data, left = None, right = None):
      self.val = data
      self.left = left
      self.right = right
class Solution:
   def solve(self, root, moves):
      past = []
      for move in moves:
         past.append(root)
         if move == "L":
            root = root.left
         elif move == "R":
            root = root.right
         else:
            past.pop()
            root = past.pop()
      return root.val
ob = Solution()
root = TreeNode(2)
root.right = TreeNode(4)
root.right.left = TreeNode(3)
root.right.right = TreeNode(5)
traverse = ["R","R","U","L"]
print(ob.solve(root, traverse))

Input

root = TreeNode(2) root.right = TreeNode(4) root.right.left =
TreeNode(3) root.right.right = TreeNode(5) ["R","R","U","L"]

Output

3