Chapter 8 Exercise 24, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

 

*8.24 (Check Sudoku solution) Listing 8.4 checks whether a solution is valid by checking whether every number is valid in the board. Rewrite the program by checking whether every row, every column, and every small box has the numbers 1 to 9.

import java.util.Scanner;
 
 
public class ProgrammingEx8_24 {
 
 public static void main(String[] args) {
     // Read a Sudoku solution
     int[][] grid = readASolution();
 
     System.out.println(isValid(grid) ? "Valid solution" :
       "Invalid solution");
   }
    
   private static boolean isValid(int[][] grid) {
 
    return checkBlocks(grid) && checkRow(grid) && checkCol(grid);
 }
 
 /** Read a Sudoku solution from the console */
   public static int[][] readASolution() {
     // Create a Scanner
     Scanner input = new Scanner(System.in);
 
     System.out.println("Enter a Sudoku puzzle solution:");
     int[][] grid = new int[9][9];
     for (int i = 0; i < 9; i++) 
       for (int j = 0; j < 9; j++)
         grid[i][j] = input.nextInt();
      
     return grid;
   }
  
 public static boolean checkBlocks( int n[][]) {
  for (int i = 0; i < n.length; i+=3) {
   for (int j = 0; j < n[i].length; j+=3) {
    if (!checkBlock(i,j,n)){
     return false;
    }
   }
  }
  return true;
 }
  
 
 public static boolean checkBlock(int row, int col, int[][] n) {
  int[] seq = new int[9];
  for (int i = 0; i < seq.length; i++) {
   seq[i] = n[i/3][i%3];
  }
  return checkSeq(seq);
 }
  
 public static boolean checkRow(int n[][]) {
  int[] seq = new int[9];
  for (int i = 0; i < n.length; i++) {
   for (int j = 0; j < n.length; j++) {
    seq[j] = n[i][j];
   }
   if(!checkSeq(seq)) {
    return false;
   }
  }
  return true;
 }
 public static boolean checkCol(int n[][]) {
  int[] seq = new int[9];
  for (int i = 0; i < n.length; i++) {
   for (int j = 0; j < n.length; j++) {
    seq[j] = n[j][i];
   }
   if(!checkSeq(seq)) {
    return false;
   }
  }
  return true;
 }
 //Check a sequence of 9 numbers if it contain number 1-9
 public static boolean checkSeq(int n[]) {
  boolean[] tray = new boolean [n.length];
  boolean result =true;
   
  for (int i = 0; i < tray.length; i++) {
   tray[n[i]-1] = true; 
  }
   
  for (int j = 0; j < tray.length; j++) {
   result &= tray[j];
  }
   
  return result;
 }
 
 
}