Rope Data Structure for Strings in JavaScript

Ropes are a data structure used to efficiently represent and manipulate large strings. Unlike traditional strings, which are stored contiguously in memory, ropes are represented as a tree of smaller strings, allowing for faster concatenation, splitting, and substring operations, especially for very large strings. This challenge asks you to implement a basic Rope data structure in JavaScript.

Problem Description

You are tasked with creating a Rope class in JavaScript that represents a string as a tree of smaller strings (nodes). The Rope class should support the following operations:

• constructor(str): Initializes a Rope object with an initial string. If the input string is empty, the rope should be an empty leaf node.
• concat(otherRope): Concatenates the current Rope with another Rope object, returning a new Rope representing the combined string.
• substring(startIndex, endIndex): Returns a new Rope representing a substring of the original string, from startIndex (inclusive) to endIndex (exclusive).
• toString(): Returns the string representation of the Rope. This should traverse the tree and concatenate all leaf nodes.

The internal representation of the Rope should be a binary tree where each node contains either a string (leaf node) or two child Rope objects (internal node). The goal is to optimize operations like concatenation and substring extraction by minimizing the number of string copies and traversals.

Key Requirements:

• The Rope class must be implemented.
• The concat, substring, and toString methods must function correctly.
• The internal tree structure should be maintained correctly.
• Consider the case where the input string to the constructor is very large.

Expected Behavior:

The Rope class should behave as if it were a string, but with optimized performance for large strings and frequent modifications. The toString() method should always return the correct string representation, regardless of the internal tree structure.

Edge Cases to Consider:

• Empty input strings to the constructor.
• startIndex and endIndex out of bounds in substring. Handle these gracefully (e.g., return an empty rope or throw an error, as you deem appropriate, but document your choice).
• startIndex greater than endIndex in substring.
• Concatenating multiple ropes together.
• Repeated substring operations.

Examples

Example 1:

Input:
rope1 = new Rope("hello");
rope2 = new Rope(" world");
result = rope1.concat(rope2);
console.log(result.toString());
Output: "hello world"
Explanation: The two ropes are concatenated to form a new rope representing "hello world".

Example 2:

Input:
rope = new Rope("This is a very long string to test the rope data structure.");
substringRope = rope.substring(5, 20);
console.log(substringRope.toString());
Output: "is a very lo"
Explanation: A substring from index 5 to 20 is extracted and represented as a new rope.

Example 3:

Input:
rope = new Rope("");
console.log(rope.toString());
Output: ""
Explanation: An empty rope is created and its string representation is an empty string.

Constraints

• The maximum length of a string stored in a leaf node should be limited to 1024 characters. If the initial string passed to the constructor is longer than this, split it into smaller strings of at most 1024 characters.
• The input string to the constructor will be a string.
• startIndex and endIndex in substring will be non-negative integers.
• Performance: While a fully optimized rope implementation is complex, aim for reasonable performance, especially for concatenation and substring operations on large ropes. Avoid unnecessary string copies.

Notes

• Consider using recursion to traverse the rope tree.
• Think about how to efficiently split a long string into smaller chunks for leaf nodes.
• The internal tree structure is not exposed to the user; only the public methods are required.
• Error handling for invalid input (e.g., negative indices in substring) is acceptable, but should be clearly documented. You can choose to throw errors or return empty ropes.
• Focus on the core functionality of the Rope class. Advanced features like indexing or character replacement are not required for this challenge.