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SudokuSolverServlet.java
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SudokuSolverServlet.java
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// file description -----------------------------------------------------------
// filename: SudokuSolverServlet.java
//
// author: Arsalan Sufi
//
// description:
//
// The SudokuSolverServlet class processes the information entered into the web
// app's HTML form. It then checks if the entered Sudoku is solvable. If so, it
// implements a backtracking algorithm to solve it and sends the solution in an
// HTML response.
// import statements ----------------------------------------------------------
package sudokusolver;
import java.io.IOException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
// SudokuSolverServlet class --------------------------------------------------
@SuppressWarnings("serial")
public class SudokuSolverServlet extends HttpServlet {
// doGet() and doPost() methods -------------------------------------------
// public void doGet()
//
// parameters:
// -- HttpServletRequest req --
// The servlet request object.
// -- HttpServletResponse resp --
// The servlet response object.
//
// This method handles get requests and is the primary method in this
// class.
//
public void doGet(HttpServletRequest req, HttpServletResponse resp)
throws IOException {
// Store Sudoku as 2D array obtaining input from HTML form.
int[][] sudoku = new int[9][9];
for (int row = 0; row < 9; row++) {
for (int column = 0; column < 9; column++) {
String inputBox = "n" + ((column + 1) + row * 9);
if ( req.getParameter(inputBox).equals("")
|| req.getParameter(inputBox).equals(null)) {
sudoku[row][column] = 0;
} else {
sudoku[row][column] = Integer.parseInt(
req.getParameter(inputBox));
}
}
}
// Set default prompt.
String prompt = "Huzzah!<br>Success!<br>I solved it!<br>Try another?" +
"<br><br>";
// Solve Sudoku if valid.
if (isValidSudoku(sudoku)) {
// Store Sudoku's initial state in separate array.
int[][] sudokuInitial = new int[9][9];
for (int row = 0; row < 9; row++) {
for (int column = 0; column < 9; column++) {
sudokuInitial[row][column] = sudoku[row][column];
}
}
solve(sudoku, sudokuInitial);
// Don't solve Sudoku if invalid and adjust prompt accordingly.
} else {
prompt = "Sorry... I<br>couldn’t solve<br>this one. Try" +
"<br>another?<br><br>";
}
// Delay procession of program to allow time for JavaScript animation.
long start = System.currentTimeMillis();
long end = start + 3000;
while (System.currentTimeMillis() < end) ;
sendResponse(resp, sudoku, prompt);
}
// public void doPost()
//
// parameters:
// -- HttpServletRequest req --
// The servlet request object.
// -- HttpServletResponse resp --
// The servlet response object.
//
// This method redirects post requests to the doGet() method.
//
public void doPost(HttpServletRequest req, HttpServletResponse resp)
throws IOException {
doGet(req, resp);
}
// high-level methods -----------------------------------------------------
// public static boolean isValidSudoku()
//
// parameters:
// -- int[][] sudoku --
// The Sudoku puzzle in consideration stored as a 2D array.
//
// This method checks if {sudoku} is solvable.
//
public static boolean isValidSudoku(int[][] sudoku) {
int numToCheck = 0;
for (int row = 0; row < 9; row++) {
for (int column = 0; column < 9; column++) {
if (sudoku[row][column] != 0) {
numToCheck = sudoku[row][column];
sudoku[row][column] = 0;
if (!isPossible(sudoku, row, column, numToCheck)) {
sudoku[row][column] = numToCheck;
return false;
} else {
sudoku[row][column] = numToCheck;
}
}
}
}
return true;
}
// public static void solve()
//
// parameters:
// -- int[][] sudoku --
// The Sudoku puzzle in consideration stored as a 2D array.
// -- int[][] sudokuInitial --
// The initial state of the Sudoku puzzle stored as a 2D array.
//
// This method solves {sudoku}. It implements a tail-recursive backtracking
// algorithm using a while loop.
//
public static void solve(int[][] sudoku, int[][] sudokuInitial) {
// Find first blank square.
int row = 0;
int column = 0;
outerLoop:
for (row = 0; row < 9; row++) {
for (column = 0; column < 9; column++) {
if (sudoku[row][column] == 0) break outerLoop;
}
}
// Loop until {sudoku} represents a solution.
while (row != 9) {
// Place value other than current value in square if possible.
int initialValue = sudoku[row][column];
for (int numToCheck = initialValue + 1;
numToCheck <= 9;
numToCheck++) {
if (isPossible(sudoku, row, column, numToCheck)) {
sudoku[row][column] = numToCheck;
break;
}
}
// Backtrack if no other value is possible.
if (sudoku[row][column] == initialValue) {
sudoku[row][column] = 0;
do {
if (column != 0) {
column--;
} else {
row--;
column = 8;
}
} while (sudokuInitial[row][column] != 0);
// Otherwise move on to next empty square.
} else {
do {
if (column != 8) {
column++;
} else {
row++;
column = 0;
}
if (row == 9) break;
} while (sudokuInitial[row][column] != 0);
}
}
}
// public static void sendResponse()
//
// parameters:
// -- HttpServletResponse resp --
// The servet response object.
// -- int[][] sudoku --
// The solved Sudoku stored in a 2D array. If the Sudoku wasn't
// solvable, this variable contains the initial Sudoku.
// -- String prompt --
// The prompt for the user. Varies depending on whether or not the
// entered Sudoku was solvable.
//
// This method sends the solution (if found) and associated prompt in an
// HTML response.
//
// TODO: Use the repetition in the response to clean this method up.
//
public static void sendResponse(HttpServletResponse resp,
int[][] sudoku, String prompt)
throws IOException {
resp.setContentType("text/html");
resp.getWriter().print(
"\n" +
"<table id=\"subContainer\">\n" +
"<tr>\n" +
"\n" +
" <td>\n" +
" <table id=\"sudoku\">\n" +
" <tr>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 0, 0) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 0, 1) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 0, 2) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 0, 3) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 0, 4) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 0, 5) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 0, 6) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 0, 7) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 0, 8) + "</td>\n" +
" </tr>\n" +
" <tr>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 1, 0) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 1, 1) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 1, 2) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 1, 3) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 1, 4) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 1, 5) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 1, 6) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 1, 7) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 1, 8) + "</td>\n" +
" </tr>\n" +
" <tr>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 2, 0) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 2, 1) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 2, 2) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 2, 3) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 2 ,4) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 2, 5) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 2, 6) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 2, 7) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 2, 8) + "</td>\n" +
" </tr>\n" +
" <tr>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 3, 0) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 3, 1) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 3, 2) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 3, 3) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 3, 4) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 3, 5) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 3, 6) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 3, 7) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 3, 8) + "</td>\n" +
" </tr>\n" +
" <tr>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 4, 0) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 4, 1) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 4, 2) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 4, 3) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 4, 4) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 4, 5) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 4, 6) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 4, 7) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 4, 8) + "</td>\n" +
" </tr>\n" +
" <tr>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 5, 0) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 5, 1) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 5, 2) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 5, 3) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 5, 4) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 5, 5) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 5, 6) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 5, 7) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 5, 8) + "</td>\n" +
" </tr>\n" +
" <tr>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 6, 0) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 6, 1) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 6, 2) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 6, 3) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 6, 4) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 6, 5) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 6, 6) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 6, 7) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 6, 8) + "</td>\n" +
" </tr>\n" +
" <tr>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 7, 0) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 7, 1) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 7, 2) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 7, 3) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 7, 4) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 7, 5) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 7, 6) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 7, 7) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 7, 8) + "</td>\n" +
" </tr>\n" +
" <tr>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 8, 0) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 8, 1) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 8, 2) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 8, 3) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 8, 4) + "</td>\n" +
" <td class=\"number-middle\">" + valueInTd(sudoku, 8, 5) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 8, 6) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 8, 7) + "</td>\n" +
" <td class=\"number\">" + valueInTd(sudoku, 8, 8) + "</td>\n" +
" </tr>\n" +
" </table>\n" +
" </td>\n" +
"\n" +
" <td id=\"verticalGap\"></td>\n" +
"\n" +
" <td id=\"instructions\">\n" +
" " + prompt + "\n" +
" <button id=\"reset\">Reset</button>\n" +
" </td>\n" +
"\n" +
"</tr>\n" +
"</table>\n" +
"\n" +
"<div class=\"horizontalGapLarge\"></div>\n" +
"\n" +
"<div class=\"homeLinkContainer\">\n" +
" <img class=\"homeLink\" src=\"Arrow.png\"/>\n" +
"</div>\n" +
"\n" +
"<div class=\"horizontalGapLarge\"></div>\n" +
"\n");
}
// low-level helper methods -----------------------------------------------
// public static boolean isPossible()
//
// parameters:
// -- int[][] sudoku --
// The sudoku puzzle in consideration stored as a 2D array.
// -- int row --
// The row number of the square in consideration.
// -- int column --
// The column number of the square in consideration.
// -- int numToCheck --
// The number to check.
//
// This method determines whether {numToCheck} can be placed in the square
// designated by {row} and {column}. The method is used by isValidSudoku()
// and solve().
//
public static boolean isPossible(int[][] sudoku,
int row, int column,
int numToCheck) {
// Set default value.
boolean memory = true;
// Check if {numToCheck} already exists in row.
for (int i = 0; i < 9; i++) {
if (sudoku[row][i] == numToCheck) memory = false;
}
// Check if {numToCheck} already exists in column.
for (int i = 0; i < 9; i++) {
if (sudoku[i][column] == numToCheck) memory = false;
}
// Check if number already exists in 3-by-3 box.
for (int i = (row / 3) * 3; i < (row / 3) * 3 + 3; i++) {
for (int j = (column / 3) * 3; j < (column / 3) * 3 + 3; j++) {
if (sudoku[i][j] == numToCheck) memory = false;
}
}
return memory;
}
// public static String valueInTd()
//
// parameters:
// -- int[][] sudoku --
// The sudoku puzzle in consideration stored as a 2D array.
// -- int row --
// The row number of the square in consideration.
// -- int column --
// The column number of the square in consideration.
//
// This method replaces the zeros in {sudoku} with blank squares.
//
public static String valueInTd(int[][] sudoku, int row, int column) {
if (sudoku[row][column] == 0) {
return "";
} else {
return "" + sudoku[row][column];
}
}
}