Sodoku.js

/**
 * Created by Albert Hoan on 2/28/2017.
 */

	function solveSudoku(board) {
		if (board == null || board.length == 0)
			return;
		solve(board);
	}

	function solve(board) {
		for (var i = 0; i < board.length; i++) {
			for (var j = 0; j < board[0].length; j++) {
				if (board[i][j] == '.') {
					for (var 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;
	}

	function isValid(board, row, col, c) {
		for (var 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 * (row / 3) + i / 3][3 * (col / 3) + i % 3] != '.' &&
				board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] == c) return false; //check 3*3 block
		}
		return true;
	}