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Design a Text Editor

Difficulty: Hard

Problem Description

Design a text editor with a cursor that can add text at the cursor's position, delete text from the left of the cursor, and move the cursor left or right. The cursor cannot move beyond the limits of the current text.

Key Insights

  • The text editor maintains a mutable string and a cursor position.
  • The addText operation appends text before the cursor and moves the cursor.
  • The deleteText operation removes characters to the left of the cursor, returning the number of characters deleted.
  • Cursor movements are constrained to the bounds of the current text, ensuring the cursor position remains valid.

Space and Time Complexity

Time Complexity: O(k) for addText and deleteText, O(1) for cursor movements.
Space Complexity: O(n) where n is the total length of the text.

Solution

To implement the text editor, we can use a list to represent the text for efficient insertions and deletions. The cursor position will be tracked as an integer index. The addText function will insert characters at the cursor, deleteText will remove characters to the left of the cursor, and the cursor movement functions will adjust the cursor position accordingly. The returned string for the left and right cursor movements will be derived from slicing the list.

Code Solutions

class TextEditor:
    def __init__(self):
        self.text = []
        self.cursor = 0

    def addText(self, text: str) -> None:
        self.text[self.cursor:self.cursor] = list(text)
        self.cursor += len(text)

    def deleteText(self, k: int) -> int:
        delete_count = min(k, self.cursor)
        self.cursor -= delete_count
        del self.text[self.cursor:self.cursor + delete_count]
        return delete_count

    def cursorLeft(self, k: int) -> str:
        self.cursor = max(0, self.cursor - k)
        return ''.join(self.text[max(0, self.cursor - 10):self.cursor])

    def cursorRight(self, k: int) -> str:
        self.cursor = min(len(self.text), self.cursor + k)
        return ''.join(self.text[max(0, self.cursor - 10):self.cursor])
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