Design a Text Editor

Design a Text Editor is a Hard Data Structures and Algorithms interview problem you can solve, run and submit on Thita.ai. It belongs to the Design Patterns pattern, in the Design (General/Specific) subpattern.

Problem statement

Design a text editor with a cursor that can do the following:

- Add text to where the cursor is.

- Delete text from where the cursor is (simulating the backspace key).

- Move the cursor either left or right.

When deleting text, only characters to the left of the cursor will be deleted. The cursor will also remain within the actual text and cannot be moved beyond it. More formally, we have that 0 <= cursor.position <= currentText.length always holds.

Implement the TextEditor class:

- TextEditor() Initializes the object with empty text.

- void addText(string text) Appends text to where the cursor is. The cursor ends to the right of text.

- int deleteText(int k) Deletes k characters to the left of the cursor. Returns the number of characters actually deleted.

- string cursorLeft(int k) Moves the cursor to the left k times. Returns the last min(10, len) characters to the left of the cursor, where len is the number of characters to the left of the cursor.

- string cursorRight(int k) Moves the cursor to the right k times. Returns the last min(10, len) characters to the left of the cursor, where len is the number of characters to the left of the cursor.

Example 1:

Input ["TextEditor", "addText", "deleteText", "addText", "cursorRight", "cursorLeft", "deleteText", "cursorLeft", "cursorRight"] [[], ["leetcode"], [4], ["practice"], [3], [8], [10], [2], [6]] Output [null, null, 4, null, "etpractice", "leet", 4, "", "practi"]

Explanation TextEditor textEditor = new TextEditor(); // The current text is "|". (The '|' character represents the cursor) textEditor.addText("leetcode"); // The current text is "leetcode|". textEditor.deleteText(4); // return 4 // The current text is "leet|". // 4 characters were deleted. textEditor.addText("practice"); // The current text is "leetpractice|". textEditor.cursorRight(3); // return "etpractice" // The current text is "leetpractice|". // The cursor cannot be moved beyond the actual text and thus did not move. // "etpractice" is the last 10 characters to the left of the cursor. textEditor.cursorLeft(8); // return "leet" // The current text is "leet|practice". // "leet" is the last min(10, 4) = 4 characters to the left of the cursor. textEditor.deleteText(10); // return 4 // The current text is "|practice". // Only 4 characters were deleted. textEditor.cursorLeft(2); // return "" // The current text is "|practice". // The cursor cannot be moved beyond the actual text and thus did not move. // "" is the last min(10, 0) = 0 characters to the left of the cursor. textEditor.cursorRight(6); // return "practi" // The current text is "practi|ce". // "practi" is the last min(10, 6) = 6 characters to the left of the cursor.

Constraints:

- 1 <= text.length, k <= 40

- text consists of lowercase English letters.

- At most 2 104 calls in total will be made to addText, deleteText, cursorLeft and cursorRight.

Follow-up: Could you find a solution with time complexity of O(k) per call?

Topics and companies

Topics: Linked List, String, Stack, Design, Simulation, Doubly-Linked List.

How to practise Design a Text Editor on Thita.ai

Starter code is provided in C, C#, C++, Go, Java, JavaScript and Python. Your solution runs against 5 test cases for this problem, with the AI coach available for a hint when you are stuck rather than a finished answer. The reference solution runs in O(k) per operation, where k is the number of characters to add, delete, or move. All operations (addText, deleteText, cursorLeft, cursorRight) are O(k) because they only move/add/delete up to k characters per call. time and O(N), where N is the total number of characters in the text editor. We store all characters in two vectors (left and right), but their total size is always N. space.

Open Design a Text Editor in the code editor, or read the Design a Text Editor editorial for a worked solution with its approach and complexity analysis.

Where Design a Text Editor sits in the DSA pattern sheet

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