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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

Program to traverse binary tree using list of directions in Python

["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

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