Sudoku Solver

Description

Write a program to solve a Sudoku puzzle by filling the empty cells.

A sudoku solution must satisfy all of the following rules:

1. Each of the digits 1-9 must occur exactly once in each row.
2. Each of the digits 1-9 must occur exactly once in each column.
3. Each of the the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid.

Empty cells are indicated by the character '.'.

A sudoku puzzle...

...and its solution numbers marked in red.

Note:

• The given board contain only digits 1-9 and the character '.'.
• You may assume that the given Sudoku puzzle will have a single unique solution.
• The given board size is always 9x9.

Solution(javascript)

/**
 * @param {character[][]} board
 * @return {void} Do not return anything, modify board in-place instead.
 */
var solveSudoku = function(board) {
    function isValid(board, row, col, c){
        for(let i = 0; i < 9; i++) {
            if(board[i][col] != '.' && board[i][col] == c) return false; //check row
            if(board[row][i] != '.' && board[row][i] == c) return false; //check column
            if(board[3 * Math.floor(row/3) + Math.floor(i/3)][ 3 * Math.floor(col/3) + i % 3] != '.' && board[3 * Math.floor(row/3) + Math.floor(i/3)][3 * Math.floor(col/3) + i % 3] == c) return false; //check 3*3 block
        }
        return true;
    }
    
    function solve(board){
        for(let i = 0; i < board.length; i++){
            for(let j = 0; j < board[0].length; j++){
                if(board[i][j] == '.'){
                    for(let c = '1'; c <= '9'; c++){//trial. Try 1 through 9
                        if(isValid(board, i, j, c)){
                            board[i][j] = '' + c; //Put c for this cell
                            
                            if(solve(board))
                                return true; //If it's the solution return true
                            else
                                board[i][j] = '.'; //Otherwise go back
                        }
                    }
                    
                    return false;
                }
            }
        }
        return true;
    }
    
    solve(board);
};