3484. Design Spreadsheet

3484. Design Spreadsheet

Difficulty: Medium

Topics: Array, Hash Table, String, Design, Matrix, Biweekly Contest 152

A spreadsheet is a grid with 26 columns (labeled from 'A' to 'Z') and a given number of rows. Each cell in the spreadsheet can hold an integer value between 0 and 105.

Implement the Spreadsheet class:

• Spreadsheet(int rows) Initializes a spreadsheet with 26 columns (labeled 'A' to 'Z') and the specified number of rows. All cells are initially set to 0.
• void setCell(String cell, int value) Sets the value of the specified cell. The cell reference is provided in the format "AX" (e.g., "A1", "B10"), where the letter represents the column (from 'A' to 'Z') and the number represents a 1-indexed row.
• void resetCell(String cell) Resets the specified cell to 0.
• int getValue(String formula) Evaluates a formula of the form "=X+Y", where X and Y are either cell references or non-negative integers, and returns the computed sum.

Note: If getValue references a cell that has not been explicitly set using setCell, its value is considered 0.

Example 1:

• Input:

  ["Spreadsheet", "getValue", "setCell", "getValue", "setCell", "getValue", "resetCell", "getValue"]
  [[3], ["=5+7"], ["A1", 10], ["=A1+6"], ["B2", 15], ["=A1+B2"], ["A1"], ["=A1+B2"]]

• Output: [null, 12, null, 16, null, 25, null, 15]
• Explanation:

  Spreadsheet spreadsheet = new Spreadsheet(3); // Initializes a spreadsheet with 3 rows and 26 columns
  spreadsheet.getValue("=5+7"); // returns 12 (5+7)
  spreadsheet.setCell("A1", 10); // sets A1 to 10
  spreadsheet.getValue("=A1+6"); // returns 16 (10+6)
  spreadsheet.setCell("B2", 15); // sets B2 to 15
  spreadsheet.getValue("=A1+B2"); // returns 25 (10+15)
  spreadsheet.resetCell("A1"); // resets A1 to 0
  spreadsheet.getValue("=A1+B2"); // returns 15 (0+15)

Constraints:

• 1 <= rows <= 103
• 0 <= value <= 105
• The formula is always in the format "=X+Y", where X and Y are either valid cell references or non-negative integers with values less than or equal to 105.
• Each cell reference consists of a capital letter from 'A' to 'Z' followed by a row number between 1 and rows.
• At most 104 calls will be made in total to setCell, resetCell, and getValue.

Hint:

1. Use a hashmap to represent the cells, where the key is the cell reference (e.g., "A1") and the value is the integer stored in the cell.
2. For setCell, simply assign the given value to the specified cell in the hashmap.
3. For resetCell, set the value of the specified cell to 0 in the hashmap.
4. For getValue, find the values of the operands from the hashmap and return their sum.

Solution:

We need to design a spreadsheet class that supports setting cell values, resetting cell values, and evaluating formulas that sum two operands, which can be either cell references or integers. The key challenge is efficiently managing cell values and parsing formulas to compute the sum correctly.

Approach

1. Initialization: The spreadsheet is initialized with a specified number of rows and 26 columns (A-Z). All cells start with a value of 0.
2. Storing Cell Values: Use a hash map (associative array in PHP) to store cell values where the key is the cell reference (e.g., "A1") and the value is the integer stored in that cell.
3. Setting Cells: When setting a cell, update its value in the hash map.
4. Resetting Cells: When resetting a cell, set its value to 0 in the hash map.
5. Evaluating Formulas: For formulas of the form "=X+Y", split the formula into two parts. For each part, check if it is a cell reference (starts with a letter followed by digits) or an integer. If it's a cell reference, retrieve its value from the hash map (defaulting to 0 if not set). If it's an integer, convert it to a number. Sum the two parts and return the result.

Let's implement this solution in PHP: 3484. Design Spreadsheet

<?php
class Spreadsheet {
    private $rows;
    private $cells;

    /**
     * @param Integer $rows
     */
    function __construct($rows) {
       ...
       ...
       ...
       /**
        * go to ./solution.php
        */
    }

    /**
     * @param String $cell
     * @param Integer $value
     * @return NULL
     */
    function setCell($cell, $value) {
       ...
       ...
       ...
       /**
        * go to ./solution.php
        */
    }

    /**
     * @param String $cell
     * @return NULL
     */
    function resetCell($cell) {
       ...
       ...
       ...
       /**
        * go to ./solution.php
        */
    }

    /**
     * @param String $formula
     * @return Integer
     */
    function getValue($formula) {
       ...
       ...
       ...
       /**
        * go to ./solution.php
        */
    }
}

/**
 * Your Spreadsheet object will be instantiated and called as such:
 * $obj = Spreadsheet($rows);
 * $obj->setCell($cell, $value);
 * $obj->resetCell($cell);
 * $ret_3 = $obj->getValue($formula);
 */

// Test cases
$spreadsheet = new Spreadsheet(3);

echo $spreadsheet->getValue("=5+7") . PHP_EOL; // 12
$spreadsheet->setCell("A1", 10);
echo $spreadsheet->getValue("=A1+6") . PHP_EOL; // 16
$spreadsheet->setCell("B2", 15);
echo $spreadsheet->getValue("=A1+B2") . PHP_EOL; // 25
$spreadsheet->resetCell("A1");
echo $spreadsheet->getValue("=A1+B2") . PHP_EOL; // 15
?>

Explanation:

• Initialization: The constructor initializes the spreadsheet with the given number of rows and an empty array to store cell values.
• setCell: This method updates the value of a specified cell in the associative array.
• resetCell: This method sets the value of a specified cell to 0 in the associative array.
• getValue: This method processes the formula by first removing the leading '=' and splitting the string by '+'. Each part is checked to see if it matches the pattern of a cell reference (a letter followed by digits). If it does, the corresponding cell value is retrieved from the associative array (or 0 if not set). If it doesn't match, the part is treated as an integer and converted. The sum of the two parts is returned.

This approach efficiently manages cell values and evaluates formulas by leveraging regular expressions to distinguish between cell references and integers, ensuring correct summation based on the current state of the spreadsheet. The solution handles all constraints and edge cases as specified in the problem.

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