gistfile1.java

package sudoku;

import java.util.Random;

public class Puzzle {

  // number generator
	Random gen = new Random();

	// 9x9 puzzle
	int puzzle[][] = new int[9][9];

	// 3x3 puzzle section
	int[][] section = new int[3][3];

	public int[][] generate() {

		// add each number to the board
		for (int x = 0; x < 9; x++) {
			for (int y = 0; y < 9; y++) {

				boolean isValid = false;

				// keep generating new numbers until a valid number is found
				while (isValid == false) {

					// generate random number 1-9
					int num = gen.nextInt(9) + 1;

					// check if number is valid
					if (checkRow(num, x) == true || checkCol(num, y) == true
							|| checkSection(num, x, y) == true) {

						// add number to the board
						puzzle[x][y] = num;

						// exit loop
						isValid = true;
					}
				}
			}
		}

		return puzzle;
	}

	// check each element of the row for num, if num is found return false
	private boolean checkRow(int num, int row) {

		boolean valid = true;
		for (int i = 0; i < 9; i++) {
			if (puzzle[row][i] == num) {
				valid = false;
				break;
			}
		}

		return valid;
	}

	// check each element of the column for num, if num is found return false
	private boolean checkCol(int num, int col) {

		boolean valid = true;
		for (int i = 0; i < 9; i++) {
			if (puzzle[i][col] == num) {
				valid = false;
				break;
			}
		}

		return valid;
	}

	// check each element of the section for num, if num is found return false
	private boolean checkSection(int num, int xPos, int yPos) {

		section = getSection(xPos, yPos);

		boolean valid = true;
		for (int i = 0; i < 3; i++) {
			for (int j = 0; j < 3; j++) {
				if (puzzle[i][j] == num) {
					valid = false;
					break;
				}
			}
		}

		return valid;
	}

	// return the 3x3 section the given coordinates are in
	private int[][] getSection(int xPos, int yPos) {

		int xIndex = 0;
		int yIndex = 0;

		// get x index
		if (xPos == 0 || xPos == 3 || xPos == 6) {
			xIndex = xPos;
		} else if (xPos == 1 || xPos == 4 || xPos == 7) {
			xIndex = xPos - 1;
		} else if (xPos == 2 || xPos == 5 || xPos == 8) {
			xIndex = xPos - 2;
		}

		// get y index
		if (yPos == 0 || yPos == 3 || yPos == 6) {
			yIndex = yPos;
		} else if (yPos == 1 || yPos == 4 || yPos == 7) {
			yIndex = yPos - 1;
		} else if (yPos == 2 || yPos == 5 || yPos == 8) {
			yIndex = yPos - 2;
		}

		int i = 0;
		int j = 0;
		// extract section from puzzle
		for (int x = xIndex; x < 3; x++) {
			for (int y = yIndex; y < 3; y++) {
				puzzle[x][y] = section[i][j];
				i++;
			}
			j++;
		}

		return section;

	}
}