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Design Spreadsheet

Difficulty: Medium

Problem Description

Design a spreadsheet with 26 columns (labeled from 'A' to 'Z') and a specified number of rows. Each cell can hold an integer value between 0 and 10^5. Implement the Spreadsheet class with methods to set a cell's value, reset a cell to zero, and evaluate simple formulas of the form "=X+Y".

Key Insights

  • The spreadsheet consists of a fixed number of columns (26) and a variable number of rows.
  • Cells are referenced by a combination of a letter (column) and a number (row), e.g., "A1".
  • Formulas can consist of integers or cell references and must be evaluated correctly.
  • Default values for cells that haven't been set are considered as 0.

Space and Time Complexity

Time Complexity:

  • O(1) for setCell and resetCell since they perform direct assignments.
  • O(1) for getValue as it involves simple string parsing and conditional checks. Space Complexity:
  • O(rows) for storing cell values, where rows is the number of rows in the spreadsheet.

Solution

To implement the Spreadsheet class, we can use a 2D array (or a dictionary) to store the values of the cells. Each cell can be accessed using its column and row indices, derived from the cell reference (e.g., "A1" translates to column 0 and row 0). The setCell method updates the value in the array, resetCell sets the value to zero, and getValue parses the formula to compute and return the result using arithmetic operations on either integers or the values stored in the cells.

Code Solutions

class Spreadsheet:
    def __init__(self, rows: int):
        # Initialize a 2D list to hold cell values
        self.rows = rows
        self.cells = [[0] * 26 for _ in range(rows)]  # 26 columns (A-Z)

    def setCell(self, cell: str, value: int) -> None:
        # Convert cell reference to indices
        col = ord(cell[0]) - ord('A')  # Column index
        row = int(cell[1:]) - 1  # Row index (1-indexed to 0-indexed)
        self.cells[row][col] = value  # Set the cell value

    def resetCell(self, cell: str) -> None:
        # Reset the specified cell to 0
        col = ord(cell[0]) - ord('A')
        row = int(cell[1:]) - 1
        self.cells[row][col] = 0  # Reset the cell value

    def getValue(self, formula: str) -> int:
        # Evaluate the formula
        # Remove leading '=' sign
        formula = formula[1:]
        x, y = formula.split('+')  # Split by '+'
        
        # Function to get value from either a cell reference or an integer
        def get_value(val):
            if val.isdigit():  # if it's a number
                return int(val)
            else:  # it's a cell reference
                col = ord(val[0]) - ord('A')
                row = int(val[1:]) - 1
                return self.cells[row][col]
        
        # Calculate and return the sum of both parts
        return get_value(x) + get_value(y)
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