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2096. Step-By-Step Directions From a Binary Tree Node to Another

Difficulty Topics

Description

You are given the root of a binary tree with n nodes. Each node is uniquely assigned a value from 1 to n. You are also given an integer startValue representing the value of the start node s, and a different integer destValue representing the value of the destination node t.

Find the shortest path starting from node s and ending at node t. Generate step-by-step directions of such path as a string consisting of only the uppercase letters 'L', 'R', and 'U'. Each letter indicates a specific direction:

  • 'L' means to go from a node to its left child node.
  • 'R' means to go from a node to its right child node.
  • 'U' means to go from a node to its parent node.

Return the step-by-step directions of the shortest path from node s to node t.

 

Example 1:

Input: root = [5,1,2,3,null,6,4], startValue = 3, destValue = 6
Output: "UURL"
Explanation: The shortest path is: 3 → 1 → 5 → 2 → 6.

Example 2:

Input: root = [2,1], startValue = 2, destValue = 1
Output: "L"
Explanation: The shortest path is: 2 → 1.

 

Constraints:

  • The number of nodes in the tree is n.
  • 2 <= n <= 105
  • 1 <= Node.val <= n
  • All the values in the tree are unique.
  • 1 <= startValue, destValue <= n
  • startValue != destValue

Solution

step-by-step-directions-from-a-binary-tree-node-to-another.py
# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right

class Solution:
    def getDirections(self, root: Optional[TreeNode], startValue: int, destValue: int) -> str:
        nodes = collections.defaultdict(tuple)

        def go(node, parent):
            if not node: return

            nodes[node.val] = (parent, node)

            go(node.left, node.val)
            go(node.right, node.val)

        go(root, -1)

        deq = collections.deque([(startValue, "")])
        visited = set([startValue])

        while deq:
            x, path = deq.popleft()

            if x == destValue: return path

            if x == -1: continue
            parent, node = nodes[x]

            if parent not in visited:
                visited.add(parent)
                deq.append((parent, path + "U"))

            if node.left and node.left.val not in visited:
                visited.add(node.left.val)
                deq.append((node.left.val, path + "L"))

            if node.right and node.right.val not in visited:
                visited.add(node.right.val)
                deq.append((node.right.val, path + "R"))