Design a Text Editor

Design a text editor that supports text manipulation and cursor navigation operations efficiently with linked-list-based data structures.

linked list string stack design simulation

Problem Statement

You are tasked with designing a text editor that supports multiple operations with a cursor. The supported operations are adding text, deleting text, and moving the cursor left or right. The cursor should never move outside the bounds of the text, and deletions should only occur left of the cursor. A doubly-linked list is a useful data structure for managing the text and cursor position efficiently.

You will implement the TextEditor class that provides the following methods: addText(text: string), deleteText(k: number), cursorLeft(k: number), cursorRight(k: number). Each method performs the described operation. When adding or deleting text, the cursor should stay within bounds. The goal is to handle up to 20,000 operations efficiently.

Examples

Example 1

Input: See original problem statement.

Output: See original problem statement.

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.

Solution Approach

Using Doubly-Linked List

To handle cursor movements and text modifications efficiently, we can use a doubly-linked list. Each node represents a character, and the cursor is a pointer to a specific node. Operations like adding text and deleting text become simpler by adjusting pointers, while maintaining the invariant that the cursor never exceeds the bounds of the text.

Efficiently Managing Operations

Each operation (adding text, deleting text, moving the cursor) should ideally be done in constant time. This is achieved by directly manipulating the linked list's nodes. Adding or deleting characters can be done by modifying the node connections, and moving the cursor involves traversing a few nodes.

Edge Cases and Boundaries

Handle edge cases where the cursor cannot move beyond the text bounds or where deletions go out of range. Ensure that the cursor moves correctly even when the length of the text changes due to delete or add operations. Special attention is needed when the cursor is near the start or end of the text.

Complexity Analysis

Metric	Value
Time	Depends on the final approach
Space	Depends on the final approach

Time complexity depends on the operations and the final approach. In the worst case, adding or deleting text could involve traversing a portion of the list, making it O(n) for each operation. However, if the approach is optimized with direct node manipulation, many operations can be O(1). Space complexity is O(n) due to the storage required for the linked list nodes.

What Interviewers Usually Probe

Focus on managing text and cursor efficiently with minimal overhead.
Test edge cases where the cursor is near the start or end of the text.
Evaluate the candidate’s ability to balance between time complexity and space usage in this linked-list-based approach.

Common Pitfalls or Variants

Common pitfalls

Not handling edge cases where the cursor is at the beginning or end of the text.
Inefficiently traversing the list during cursor movements or text modifications.
Not maintaining the cursor’s position correctly when operations are interleaved.

Follow-up variants

Design a similar text editor but with undo/redo functionality.
Modify the design to support searching for a substring or replacing text.
Extend the design to support multi-cursor behavior and simultaneous edits.

FAQ

How can I efficiently design a text editor with cursor manipulation?

Use a doubly-linked list to represent the text and manage the cursor with pointers. This allows for efficient text modifications and cursor movements.

What are the main challenges in the 'Design a Text Editor' problem?

The main challenges include efficiently managing cursor movements, handling text deletions and additions, and ensuring constant-time operations on the linked list.

How does linked-list pointer manipulation apply in this text editor problem?

Linked-list pointer manipulation allows efficient insertion, deletion, and movement of text characters by directly adjusting node pointers, rather than shifting text in an array.

What operations should the TextEditor class support?

The TextEditor class should support operations like adding text, deleting text, and moving the cursor left or right within the text.

How does GhostInterview help with 'Design a Text Editor' problem-solving?

GhostInterview offers tailored explanations and interactive problem-solving approaches, helping you visualize and implement the text editor with optimal data structures.

terminal

Solution

Solution 1: Left and Right Stacks

We can use two stacks, $\textit{left}$ and $\textit{right}$, where the stack $\textit{left}$ stores the characters to the left of the cursor, and the stack $\textit{right}$ stores the characters to the right of the cursor.

class TextEditor:
    def __init__(self):
        self.left = []
        self.right = []

    def addText(self, text: str) -> None:
        self.left.extend(list(text))

    def deleteText(self, k: int) -> int:
        k = min(k, len(self.left))
        for _ in range(k):
            self.left.pop()
        return k

    def cursorLeft(self, k: int) -> str:
        k = min(k, len(self.left))
        for _ in range(k):
            self.right.append(self.left.pop())
        return ''.join(self.left[-10:])

    def cursorRight(self, k: int) -> str:
        k = min(k, len(self.right))
        for _ in range(k):
            self.left.append(self.right.pop())
        return ''.join(self.left[-10:])


# Your TextEditor object will be instantiated and called as such:
# obj = TextEditor()
# obj.addText(text)
# param_2 = obj.deleteText(k)
# param_3 = obj.cursorLeft(k)
# param_4 = obj.cursorRight(k)

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