How do you solve Flip Binary Tree To Match Preorder Traversal on LeetCode?

Flip Binary Tree To Match Preorder Traversal (LeetCode #971) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Flipping nodes is necessary only when the left child does not match the expected value in the voyage.

What is the time complexity of Flip Binary Tree To Match Preorder Traversal?

The optimal solution for Flip Binary Tree To Match Preorder Traversal runs in O(n) time and uses O(n) space. The time complexity is O(n) because we traverse each node exactly once. The space complexity is O(n) due to the recursion stack in the DFS.

What is the brute force solution for Flip Binary Tree To Match Preorder Traversal?

The brute force approach for Flip Binary Tree To Match Preorder Traversal is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute-force approach involves generating all possible pre-order traversals of the binary tree by flipping nodes and checking if any of them match the given voyage. This is straightforward but inefficient. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Flip Binary Tree To Match Preorder Traversal?

Flip Binary Tree To Match Preorder Traversal uses the following concepts: Tree, Depth-First Search, Binary Tree. The recommended patterns to study are: Depth-First Search, Tree Traversal.

What are the interview tips for Flip Binary Tree To Match Preorder Traversal?

Always clarify the problem requirements and constraints before diving into coding. Think about edge cases, such as when the tree is empty or has only one node. Practice explaining your thought process as you code, as this helps in interviews.

What are common mistakes when solving Flip Binary Tree To Match Preorder Traversal?

Failing to handle cases where the current node does not match the voyage correctly. Not keeping track of the index properly during the traversal.

#971

Flip Binary Tree To Match Preorder Traversal

Medium

TreeDepth-First SearchBinary TreeDepth-First SearchTree Traversal

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

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Intuition

Time O(n)Space O(n)

The optimal solution uses depth-first search (DFS) to traverse the tree while checking against the voyage. It flips nodes only when necessary, ensuring a linear traversal of the tree.

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Algorithm

3 steps

1Step 1: Initialize an empty list for flips and set index to 0.
2Step 2: Perform a DFS traversal of the tree, comparing each node's value with the current value in the voyage.
3Step 3: If the left child exists but does not match the voyage, flip the node and continue the traversal.

solution.py25 lines

1# Full working Python code
2class TreeNode:
3    def __init__(self, val=0, left=None, right=None):
4        self.val = val
5        self.left = left
6        self.right = right
7
8class Solution:
9    def flipMatchVoyage(self, root: TreeNode, voyage: List[int]) -> List[int]:
10        flips = []
11        index = 0
12
13        def dfs(node):
14            nonlocal index
15            if not node:
16                return True
17            if node.val != voyage[index]:
18                return False
19            index += 1
20            if (node.left and index < len(voyage) and node.left.val != voyage[index]):
21                flips.append(node.val)
22                return dfs(node.right) and dfs(node.left)
23            return dfs(node.left) and dfs(node.right)
24
25        return flips if dfs(root) else [-1]

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Complexity note: The time complexity is O(n) because we traverse each node exactly once. The space complexity is O(n) due to the recursion stack in the DFS.

1Flipping nodes is necessary only when the left child does not match the expected value in the voyage.
2DFS is an effective way to traverse the tree while keeping track of the required order.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.