Valid sudoku problem in c#

Programming C#
1

A valid Sudoku problem checks whether a given 9x9 grid adheres to the rules of Sudoku. The rules are:

  1. Each row must contain the digits 1-9 without repetition.
  2. Each column must contain the digits 1-9 without repetition.
  3. Each of the nine 3x3 subgrids must contain the digits 1-9 without repetition.

Here’s a simple implementation in C# that checks if a given Sudoku board is valid:

using System;
using System.Collections.Generic;

public class SudokuValidator
{
    public static bool IsValidSudoku(char[][] board)
    {
        HashSet<string> seen = new HashSet<string>();
        
        for (int i = 0; i < 9; i++)
        {
            for (int j = 0; j < 9; j++)
            {
                char num = board[i][j];
                if (num != '.')
                {
                    // Create a unique string for each number in its context
                    string rowKey = $"{num} in row {i}";
                    string colKey = $"{num} in col {j}";
                    string boxKey = $"{num} in box {i / 3}-{j / 3}";

                    // Check if we have seen this number in the same row, column or box
                    if (!seen.Add(rowKey) || !seen.Add(colKey) || !seen.Add(boxKey))
                    {
                        return false; // If we have seen it, it's invalid
                    }
                }
            }
        }
        return true; // If we pass all checks, the Sudoku is valid
    }

    public static void Main(string[] args)
    {
        char[][] board = new char[][]
        {
            new char[] { '5', '3', '.', '.', '7', '.', '.', '.', '.' },
            new char[] { '6', '.', '.', '1', '9', '5', '.', '.', '.' },
            new char[] { '.', '9', '8', '.', '.', '.', '.', '6', '.' },
            new char[] { '8', '.', '.', '.', '6', '.', '.', '.', '3' },
            new char[] { '4', '.', '.', '8', '.', '3', '.', '.', '1' },
            new char[] { '7', '.', '.', '.', '2', '.', '.', '.', '6' },
            new char[] { '.', '6', '.', '.', '.', '.', '2', '8', '.' },
            new char[] { '.', '.', '.', '4', '1', '9', '.', '.', '5' },
            new char[] { '.', '.', '.', '.', '8', '.', '.', '7', '9' }
        };

        bool isValid = IsValidSudoku(board);
        Console.WriteLine($"The Sudoku board is valid: {isValid}");
    }
}

Explanation

  1. Data Structure:

    • A HashSet<string> is used to keep track of the numbers we have seen in the current row, column, and 3x3 subgrid.

  2. Iterate Through the Board:

    • We use two nested loops to go through each cell of the 9x9 board.

  3. Check Each Cell:

    • If a cell contains a number (not ‘.’), we create unique keys for that number based on its position: one for the row, one for the column, and one for the 3x3 box.

  4. Validity Check:

    • If adding any of these keys to the HashSet returns false, it means we’ve seen that number before in the same context, which violates Sudoku rules, and we return false.

  5. Final Result:

    • If we finish checking all cells without finding duplicates, we return true, indicating that the board is valid.

Usage

  • You can change the board variable to test different Sudoku configurations. The output will indicate whether the board is valid according to Sudoku rules.