April 25, 2022
Here is the link.
C# | Encode 1-9 digits to each row and each column and 9 3 x 3 matrix
April 19, 2022
Introduction
It takes me 10 minutes at least to write a working solution. First a hashset is created to include all digits from 1 to 9 to map for each row and each column and each of 9 3 x 3 matrix; next step is to go over each number in given matrix, and then remove it from the hashset.
The following C# code passes online judge.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace _36_valid_sudoku___encode_as_strings
{
class Program
{
static void Main(string[] args)
{
//[[".","8","7","6","5","4","3","2","1"],
//["2",".",".",".",".",".",".",".","."],
//["3",".",".",".",".",".",".",".","."],
//["4",".",".",".",".",".",".",".","."],
//["5",".",".",".",".",".",".",".","."],
//["6",".",".",".",".",".",".",".","."],
//["7",".",".",".",".",".",".",".","."],
//["8",".",".",".",".",".",".",".","."],
//["9",".",".",".",".",".",".",".","."]]
var board = new char[9][];
board[0] = new char[] { '.', '8', '7', '6', '5', '4', '3', '2', '1' };
board[1] = new char[] { '2', '.', '.', '.', '.', '.', '.', '.', '.' };
board[2] = new char[] { '3', '.', '.', '.', '.', '.', '.', '.', '.' };
board[3] = new char[] { '4', '.', '.', '.', '.', '.', '.', '.', '.' };
board[4] = new char[] { '5', '.', '.', '.', '.', '.', '.', '.', '.' };
board[5] = new char[] { '6', '.', '.', '.', '.', '.', '.', '.', '.' };
board[6] = new char[] { '7', '.', '.', '.', '.', '.', '.', '.', '.' };
board[7] = new char[] { '8', '.', '.', '.', '.', '.', '.', '.', '.' };
board[8] = new char[] { '9', '.', '.', '.', '.', '.', '.', '.', '.' };
var result = IsValidSudoku(board);
}
/// <summary>
/// study code:
/// https://leetcode.com/problems/valid-sudoku/discuss/15472/Short%2BSimple-Java-using-Strings
/// Collect the set of things we see, encoded as strings. For example:
/// '4' in row 7 is encoded as "(4)7".
/// '4' in column 7 is encoded as "7(4)".
/// '4' in the top-right block is encoded as "0(4)2".
/// </summary>
/// <param name="board"></param>
/// <returns></returns>
public static bool IsValidSudoku(char[][] board)
{
var set = new HashSet<string>();
var digits = "123456789".ToCharArray();
/*
* Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:
Each row must contain the digits 1-9 without repetition.
Each column must contain the digits 1-9 without repetition.
Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition.
*/
foreach(var digit in digits)
{
var digitStr = "(" + digit.ToString() + ")";
// add all rows - ()0-9
for (int index = 0; index < 9; ++index)
{
set.Add(digitStr + index.ToString()); // every row at most 9 distinct digits
set.Add(index.ToString() + digitStr); // every column
set.Add(index % 3 + digitStr + index / 3); // 9 3 x 3 matrixes
}
}
for (int row = 0; row < 9; ++row)
{
for (int col = 0; col < 9; ++col)
{
if (board[row][col] == '.')
{
continue;
}
var b = "(" + board[row][col] + ")";
if (set.Contains(b + row) && set.Contains(col + b) && set.Contains(row / 3 + b + col / 3))
{
set.Remove(b + row);
set.Remove(col + b);
set.Remove(row / 3 + b + col / 3);
}
else
{
return false;
}
}
}
return true;
}
}
}
