Data structure for text editor

Question

This is an interview question. What data structure would you use to store the text in a text editor?

Answer 1

Rope

A rope is essentially a binary tree whose leaves are arrays of characters. A node in the tree has a left child and a right child - the left child is the first part of the string, while the right child is the final part of the string. Concatenation of two ropes simply involves the creation of a new tree node with both ropes as children. To ensure logarithmic time indexing and sub-string operations the resulting rope may need to be balanced. Various balancing strategies are possible.

The main advantages of ropes as compared to storing strings as character arrays is that they enable much faster concatenation than ordinary strings, and don't require a large contiguous memory space to store a large string. The main disadvantages are greater overall space usage and slower indexing, both of which become more severe as the tree structure becomes larger and deeper. However, many practical applications of indexing involve only iteration over the string, which remains fast as long as the leaf nodes are large enough to benefit from cache effects.