How do you solve Construct String from Binary Tree on LeetCode?

Construct String from Binary Tree (LeetCode #606) 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: Understanding how to represent tree structures in strings is crucial for many coding problems.

What is the brute force solution for Construct String from Binary Tree?

The brute force approach for Construct String from Binary Tree is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach involves recursively traversing the binary tree in a preorder manner and constructing the string representation at each node. This method is straightforward but can be inefficient due to repeated string concatenations. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Construct String from Binary Tree?

Construct String from Binary Tree uses the following concepts: String, Tree, Depth-First Search, Binary Tree. The recommended patterns to study are: Depth-First Search, Recursion.

What are the interview tips for Construct String from Binary Tree?

Always clarify the problem statement and edge cases before jumping into coding. Think about the traversal method you will use and how it affects the string construction. Practice writing recursive functions, as they are common in tree problems.

What are common mistakes when solving Construct String from Binary Tree?

Forgetting to include empty parentheses for a right child when there's no left child. Not handling the base case for null nodes properly.

#606

Construct String from Binary Tree

Medium

StringTreeDepth-First SearchBinary TreeDepth-First SearchRecursion

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 a recursive approach similar to the brute force method but avoids unnecessary string concatenations by building the string in a more efficient manner. This ensures we only traverse the tree once and construct the string in linear time.

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Algorithm

4 steps

1Step 1: Define a recursive function that takes a node and builds the string.
2Step 2: Append the node's value to the result string.
3Step 3: If the node has a left child, append its value enclosed in parentheses.
4Step 4: If the node has a right child, check if the left child is absent and append empty parentheses if so, then append the right child's value in parentheses.

solution.py9 lines

1def tree2str(root):
2    if not root:
3        return ""
4    result = str(root.val)
5    if root.left or root.right:
6        result += f'({tree2str(root.left)})'
7    if root.right:
8        result += f'({tree2str(root.right)})' if root.left or root.right else ''
9    return result

ℹ

Complexity note: The time complexity is O(n) because we visit each node exactly once. The space complexity is O(n) due to the recursive call stack and the space used for the resulting string.

1Understanding how to represent tree structures in strings is crucial for many coding problems.
2Recognizing when to include or omit parentheses based on child presence is key to solving this problem.

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