OpenAI interview question # 3 – Implement Spreadsheet with Cells — Recursive Dependency Evaluation

Implement Spreadsheet with Cells

You are asked to design a simple Spreadsheet system consisting of multiple cells, where each cell can either contain a numeric value or depend on other cells by referencing them as children.

Each cell can be represented as an object:

class Cell {
    Integer value;
    String child1;
    String child2;
}

If a cell contains a value, it’s a constant.
If it contains one or two child references, its value equals the sum of its children.

You are required to implement a class Spreadsheet that supports:

1. Setting a cell with either a value or children references.
2. Getting the calculated value of a given cell key.

Example

Input:

setCell("A", new Cell(null, "B", "C"));
setCell("B", new Cell(3, null, null));
setCell("C", new Cell(5, null, null));

getCellValue("A") → 8

If cells have nested references:

setCell("A", new Cell(null, "B", "C"));
setCell("B", new Cell(null, "D", null));
setCell("C", new Cell(2, null, null));
setCell("D", new Cell(4, null, null));

getCellValue("A") → 6

Key Idea

• Use DFS to traverse cell dependencies recursively.
• Use memoization to cache computed results.
• For dynamic updates, maintain a reverse dependency map (parent map) to efficiently recompute affected cells.

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