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hardMachine Coding

Build a Sudoku board with validation

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01

Understand the problem

Build a 9×9 Sudoku grid that validates rows, columns and boxes.

ReactGridValidation
02

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Building a Sudoku Board with Validation in React

Mental model: A 9×9 grid of digit strings plus a given mask (which cells are fixed). Editing a non-given cell accepts only 1–9. Validation is derived: scan every row, column, and 3×3 box for duplicate digits and collect the conflicting cell keys. Cells in tha

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04

React solution

Complete solutionRun Playground
import React from 'react';
import Sudoku from './src/Sudoku';

export default function App() {
  return (
    <div style={{ fontFamily: 'sans-serif', padding: 20 }}>
      <h1>Sudoku Demo</h1>
      <p style={{ color: '#666' }}>Fill cells 1–9. Conflicts turn red.</p>
      <Sudoku />
    </div>
  );
}
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