Construct String From Binary Tree Leetcode Problem 606 [Python]

In this blog post, we will tackle the LeetCode problem titled Construct String From Binary Tree This problem falls under the category of trees and is rated as "Easy." We will provide a Python solution to this problem, along with a detailed explanation of the algorithm, time and space complexity analysis, and considerations for edge cases.

Problem Overview

The problem statement is as follows: Given the root of a binary tree, construct a string consisting of parentheses and integers from the binary tree using the preorder traversal method.

Then, return this constructed string.

The goal is to omit all unnecessary empty parentheses pairs that do not affect the one-to-one mapping relationship between the string and the original binary tree.

Let's illustrate this with an example.

Example 1:

Suppose we are given the input tree as follows:

Input: root = [1,2,3,4]

The expected output is: "1(2(4))(3)"

Explanation: Originally, it needs to be "1(2(4)())(3()())", but you need to omit all the unnecessary empty parenthesis pairs.

And it will be "1(2(4))(3)".

Example 2:

Now, consider the input tree:

Input: root = [1,2,3,null,4]

The expected output is: "1(2()(4))(3)"

Explanation: In this example, the tree is almost the same as the first one, except we cannot omit the first parenthesis pair to maintain the one-to-one mapping relationship between the input and the output.

Constraints:

• The number of nodes in the tree is in the range [1, 104].
• Node values are within the range of -1000 to 1000.

Understanding Constraints

Before we dive into the solution, let's understand the constraints mentioned in the problem:

1. Number of Nodes: The tree can have between 1 and 104 nodes.

This means that the solution should be efficient and not have exponential time complexity in terms of the number of nodes.

1. Node Values: The values of the tree nodes can range from -1000 to 1000. This indicates that we need to handle both positive and negative integers in the tree.

With these constraints in mind, let's proceed to the solution.

Construct String From Binary Tree LeetCode Problem Solution

Bruteforce Approach

A brute-force approach to solving this problem is to perform a preorder traversal of the binary tree and construct the string as we visit each node.

We can use a recursive function to accomplish this task.

Here is the Python code for the brute-force approach:

def tree2str(root):
    # Initialize an empty list to store the result
    result = []

    # Define a helper function for preorder traversal
    def preorder(node):
        if not node:
            return
        result.append(str(node.val))
        if node.left or node.right:
            result.append('(')
            preorder(node.left)
            result.append(')')
        if node.right:
            result.append('(')
            preorder(node.right)
            result.append(')')

    # Start the preorder traversal from the root
    preorder(root)

    # Join the result list into a single string
    return ''.join(result)

In this code, we initialize an empty list result to store the characters of the constructed string.

The preorder function is a recursive helper function for performing the preorder traversal.

We append the node values and parentheses as we traverse the tree.

Finally, we join the characters in the result list to obtain the final string.

Time and Space Complexity

The time complexity of this solution is O(n), where n is the number of nodes in the binary tree.

This is because we perform a single pass through all the nodes to construct the string.

The space complexity is also O(n) as we use the result list to store the characters of the string, and its size is proportional to the number of nodes.

Reasoning Behind Our Approach

The key to solving this problem is to perform a preorder traversal of the binary tree and construct the string while visiting each node.

We append the value of the current node, and if the node has left or right children, we enclose the subtree in parentheses.

We handle the given constraints by ensuring that the code efficiently processes the tree's nodes and correctly omits unnecessary empty parentheses pairs.

By performing a single pass through the tree, we achieve a time complexity of O(n), where n is the number of nodes, and use an additional O(n) space for the result list.

Related Interview Questions By Company:

• Ugly Number LeetCode
• Kth Largest Element In A Stream LeetCode
• Baseball Game LeetCode

Related Interview Questions By Difficulty:

• Diameter Of Binary Tree LeetCode
• Balanced Binary Tree LeetCode
• Trim A Binary Search Tree LeetCode

Related Interview Questions By Category:

• Letter Combinations Of A Phone Number LeetCode
• Reverse Bits LeetCode
• Construct Binary Tree From Preorder And Inorder Traversal LeetCode

Conclusion

In this blog post, we tackled the LeetCode problem Construct String From Binary Tree (Problem 606) and provided a Python solution to the problem.

We explained the problem statement, presented a brute-force approach, and analyzed the time and space complexity of the solution.

We hope this explanation and solution have been helpful in understanding how to approach this problem.

If you have any questions, suggestions, or comments, please feel free to share them.

You can find the original problem on LeetCode at this link.

We encourage you to explore more tree-related problems and continue your coding journey.

Happy coding!