What is the time complexity of Design Spreadsheet?

The optimal solution has a time complexity of O(1).

What data structures are used to solve Design Spreadsheet?

This problem uses Array, Hash Table, String, Design, Matrix. Understanding these concepts is essential for solving this Medium problem efficiently.

What are the key insights for solving Design Spreadsheet?

Insight 1: Efficient cell addressing is crucial. Converting cell names (e.g., "A1") to row and column indices is a common operation and must be handled correctly. Insight 2: The limited formula structure (=X+Y) simplifies parsing. We don't need a full expression parser; splitting the string by '+' and then checking if each part is a number or cell reference is sufficient.

Which companies ask LeetCode 3484. Design Spreadsheet in interviews?

This problem is frequently asked at Rippling.

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Design Spreadsheet - LeetCode 3484 Solution

Design Spreadsheet - Complete Solution Guide

Design Spreadsheet is LeetCode problem 3484, a Medium level challenge. This complete guide provides step-by-step explanations, multiple solution approaches, and optimized code in python3, java, cpp, c.

Problem Statement

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 10 5 . 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" , "

Detailed Explanation

The "Design Spreadsheet" problem requires implementing a `Spreadsheet` class that simulates basic spreadsheet functionality. The spreadsheet has a fixed number of rows and 26 columns (A-Z). The class should allow setting cell values, resetting cells to zero, and evaluating simple formulas of the form "=X+Y", where X and Y can be either cell references (e.g., "A1") or non-negative integers. The problem constraints specify the range of row numbers, cell values, and the format of formulas. A key element is that if a cell is referenced in a formula before it has been assigned a value via `setCell`, its value is assumed to be 0.

Solution Approach

The provided code implements the `Spreadsheet` class with a 2D array (`grid`) to store cell values. The `setCell` method updates the grid with the given value. The `resetCell` method sets the cell value to 0 using `setCell`. The `getValue` method parses the formula, extracts the two terms (X and Y), and evaluates each term either by retrieving the value from the grid if it's a cell reference or by parsing it as an integer. Finally, it returns the sum of the evaluated terms.

Step-by-Step Algorithm

Step 1: **Initialization:** The `Spreadsheet` constructor creates a 2D integer array (grid) of size `rows x 26` and initializes all cells to 0.
Step 2: **`setCell(cell, value)`:** Parses the `cell` string to extract the row and column indices. Updates the corresponding cell in the `grid` with the given `value`.
Step 3: **`resetCell(cell)`:** Calls `setCell` with the given `cell` and a `value` of 0.
Step 4: **`getValue(formula)`:** Removes the '=' sign from the beginning of the formula. Splits the formula string by the '+' character into two terms.
Step 5: **`_evaluate_term(term)`:** Checks if the term is a cell reference (starts with a letter A-Z) or an integer. If it's a cell reference, parses the indices, retrieves the value from the `grid`, and returns it. If it's an integer, parses it and returns it.
Step 6: **`getValue(formula)` (continued):** Evaluates both terms using `_evaluate_term`. Returns the sum of the two evaluated terms.

Key Insights

Insight 1: Efficient cell addressing is crucial. Converting cell names (e.g., "A1") to row and column indices is a common operation and must be handled correctly.
Insight 2: The limited formula structure (=X+Y) simplifies parsing. We don't need a full expression parser; splitting the string by '+' and then checking if each part is a number or cell reference is sufficient.
Insight 3: The initial state of cells matters. All cells start with a value of 0, and any read before setting a value should return 0.

Complexity Analysis

Time Complexity: O(1)

Space Complexity: O(1)

Topics

This problem involves: Array, Hash Table, String, Design, Matrix.

Companies

Asked at: Rippling.

Design Spreadsheet | LeetCode 3484

Medium

Array Hash Table String Design Matrix

Time: O(1)Space: O(1)

Solution Code

Available in:

class Spreadsheet {

    private int[][] grid;

    public Spreadsheet(int rows) {
        this.grid = new int[rows][26];
    }

    private int[] _parse_indices(String cell) {
        int col = cell.charAt(0) - 'A';
        int row = Integer.parseInt(cell.substring(1)) - 1;
        return new int[]{row, col};
    }

    public void setCell(String cell, int value) {
        int[] indices = _parse_indices(cell);
        int row = indices[0];
        int col = indices[1];
        this.grid[row][col] = value;
    }

    public void resetCell(String cell) {
        setCell(cell, 0);
    }

    private int _evaluate_term(String term) {
        if (term.charAt(0) >= 'A' && term.charAt(0) <= 'Z') {
            int[] indices = _parse_indices(term);
            int row = indices[0];
            int col = indices[1];
            return this.grid[row][col];
        } else {
            return Integer.parseInt(term);
        }
    }

    public int getValue(String formula) {
        String[] terms = formula.substring(1).split("\\+");
        int val1 = _evaluate_term(terms[0]);
        int val2 = _evaluate_term(terms[1]);
        return val1 + val2;
    }
}

/**
 * Your Spreadsheet object will be instantiated and called as such:
 * Spreadsheet obj = new Spreadsheet(rows);
 * obj.setCell(cell,value);
 * obj.resetCell(cell);
 * int param_3 = obj.getValue(formula);
 */

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Problem Info

Description

Problem 3484: Design Spreadsheet - Detailed explanation and solution approaches.

Topics

Array Hash Table String Design Matrix

Companies

Rippling

Stats

Difficulty:Medium

Languages:4

Companies:1

Problem #:3484

Problem Explanation

💡

Think Before You Code

🤔 Ask Yourself

→What is the input? What output do I need?
→Can I solve a smaller version of this problem first?
→What patterns have I seen in similar problems?

✏️ Try This First

Before looking at the solution, try to solve it on paper with a simple example!

🚀 Try on LeetCode

Solution Approach

📋

Step-by-Step Solution

6 steps

1
Step 1: **Initialization:** The `Spreadsheet` constructor creates a 2D integer array (grid) of size `rows x 26` and initializes all cells to 0.
2
Step 2: **`setCell(cell, value)`:** Parses the `cell` string to extract the row and column indices. Updates the corresponding cell in the `grid` with the given `value`.
3
Step 3: **`resetCell(cell)`:** Calls `setCell` with the given `cell` and a `value` of 0.
4
Step 4: **`getValue(formula)`:** Removes the '=' sign from the beginning of the formula. Splits the formula string by the '+' character into two terms.
5
Step 5: **`_evaluate_term(term)`:** Checks if the term is a cell reference (starts with a letter A-Z) or an integer. If it's a cell reference, parses the indices, retrieves the value from the `grid`, and returns it. If it's an integer, parses it and returns it.
6
Step 6: **`getValue(formula)` (continued):** Evaluates both terms using `_evaluate_term`. Returns the sum of the two evaluated terms.

💡

Pro Tip for Students

Try tracing through each step with a small example on paper before coding. Understanding "why" each step happens is more important than memorizing the code!

⚡

Complexity Analysis

⏱️

Time Complexity

O(1)

⚡ Constant time - Super fast! Same speed regardless of input size.

💾

Space Complexity

O(1)

💪 Constant space - Uses same memory regardless of input!

📝

Why?

All the methods (`setCell`, `resetCell`, `getValue`, and `_evaluate_term`) perform a constant number of operations. `setCell` and `resetCell` involve a constant-time array access after converting the input cell to corresponding indices. `getValue` involves string manipulation with substring and split, however due to constant length string parsing, it takes O(1) operations. `_evaluate_term` also takes O(1). Hence, the overall time complexity for all operations is O(1). Space complexity is O(rows) because the grid size is rows * 26 (26 is a constant).

📖New to Big O? Click to learn more

Big O Notation - Quick Guide

O(1)Best - Instant

O(log n)Excellent - Binary Search

O(n)Good - One loop

O(n log n)OK - Sorting

O(n²)Slow - Nested loops

O(2ⁿ)Very Slow - Recursion

Alternative Approaches

HashMap-based Spreadsheet

Instead of a 2D array, a HashMap (or Dictionary) can be used to store cell values. The key would be the cell name (e.g., "A1"), and the value would be the integer value.

Time: O(1) on average for set, reset and get. Worst case O(n) with lots of hash collisions.Space: O(n) where n is the number of cells that have been set

Trade-offs: The HashMap approach can be more space-efficient if only a small subset of the cells are used. However, it adds the overhead of HashMap operations and might have slightly worse performance in the best case scenario because array access in the provided solution is very fast. It also uses more space if a very large percentage of the cells are set. For this particular problem size (max 1000 rows), array solution is more convenient.

✨

Key Insights

1Insight 1: Efficient cell addressing is crucial. Converting cell names (e.g., "A1") to row and column indices is a common operation and must be handled correctly.
2Insight 2: The limited formula structure (=X+Y) simplifies parsing. We don't need a full expression parser; splitting the string by '+' and then checking if each part is a number or cell reference is sufficient.
3Insight 3: The initial state of cells matters. All cells start with a value of 0, and any read before setting a value should return 0.

📚

Key Terms Explained

For Students

Array

A collection of items stored at contiguous memory locations. Like a row of boxes.

Hash Table

A data structure that maps keys to values for quick lookup. Like a dictionary!

String

A sequence of characters. Like a word or sentence in programming!

Edge Cases

Edge case 1: Accessing a cell before setting its value. The code handles this correctly because the grid is initialized with all values set to 0. Therefore, any attempt to read a cell's value before setting it will return 0 as specified by the problem.
Edge case 2: Invalid cell format in `setCell` or `getValue`. The problem statement guarantees that the input cell format will be valid, so no error handling is required for this case. However, in a real-world application, input validation would be necessary.
Edge case 3: Very large number of rows. The O(rows) space complexity can become a problem. Since 'rows' is capped at 1000, this is not much of a concern within this problem's specific constraints.

⚠️

Common Mistakes to Avoid

✗Common mistake 1: Off-by-one errors when converting between cell names (e.g., "A1") and array indices. Remember that rows are 1-indexed in the problem description but 0-indexed in the array.

✗Common mistake 2: Not handling the case where a cell is read before it has been set. The grid must be initialized to 0 or a default value to avoid returning garbage data.

✗Common mistake 3: Incorrect formula parsing. It is essential to correctly extract the terms from the formula string and evaluate them appropriately.

✅

Learning Tip

Every mistake is a learning opportunity! When you make an error, understand why it happened before moving on.

🌍

Where is This Used in Real Life?

💼Real-world scenario 1: Implementing a simple spreadsheet application. This problem represents the core functionality of a spreadsheet, such as storing cell values and evaluating formulas.

🏦Real-world scenario 2: Configuration management. Storing and retrieving configuration parameters, where some parameters depend on the values of other parameters. Can also be used in game development to manage unit stats in a structured way.

🎮Real-world scenario 3: Data analysis and reporting. Creating reports where values are derived from calculations based on other data points.

💡Understanding real-world applications helps you see the "why" behind algorithms. It's not just about passing interviews—these concepts power the apps and websites you use every day!

Author's Notes

💡 Key Insight

When dealing with arrays, always consider if sorting would simplify the problem. Many array problems have O(n) solutions using hash maps or two-pointer technique.

🎯 Interview Tip

If stuck, try working through a small example by hand. The pattern often reveals itself.

⚠️ Watch Out

Off-by-one errors are the most common mistake. Double-check your loop bounds and array indices.

Written by Saswata Mondal

Software Engineer • Algorithms Enthusiast • Interview Coach

👨‍💻

About the Author

👨‍💻

Saswata MondalAuthor400+ LC Problems

B.Tech CSE, IEM Kolkata | LeetCode Rating: 1672 (Top 15%)

Certified: IBM Java Developer, NPTEL Programming in Java

Last updated: August 4, 2024LeetCode Profile GitHub

This solution has been crafted based on my experience solving 400+ LeetCode problems. Each explanation is designed to help you understand the underlying concepts, not just memorize the code.

Community Tips & Insights

In a real interview, always clarify constraints first. Ask about input size and value ranges.

@TechLeadJul 13

Don't forget to handle the edge case when the input is empty. Many candidates miss this in interviews.

@DevExpert92Jul 6

❓

Frequently Asked Questions

What is the most efficient way to solve array problems?

Most array problems can be solved efficiently using techniques like two-pointer approach, sliding window, or hash maps. The key is identifying whether the array is sorted (enabling binary search) or if tracking seen elements (using hash maps) can help achieve O(n) time complexity.

What are the trade-offs of using a hash table?

Hash tables provide O(1) average-case lookup, insertion, and deletion, making them ideal for frequency counting and duplicate detection. However, they use O(n) extra space and may degrade to O(n) time in worst-case scenarios with hash collisions. Always consider if the space trade-off is acceptable.

What techniques are commonly tested in medium-difficulty problems?

Medium problems often require combining multiple techniques: two-pointer with hash maps, BFS/DFS with state tracking, dynamic programming with optimization, or divide-and-conquer approaches. They test your ability to recognize patterns and choose the right combination of techniques.

How should I practice algorithm problems effectively?

Focus on understanding patterns rather than memorizing solutions. After solving a problem, review optimal solutions and understand the intuition. Group similar problems to recognize patterns. Practice explaining your approach out loud. Review problems after a few days to test retention.

What is the optimal approach for "Design Spreadsheet"?

For this medium-level Array problem, the key is to identify the core pattern. Analyze the input constraints to determine acceptable time complexity. Consider whether hash table techniques can optimize the solution. Always handle edge cases and validate your approach with examples before coding.

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