Android Open Source - Sudoku-Solver Solve

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Back to project page Sudoku-Solver.

License

The source code is released under:

Apache License

Java Source Code

package com.awhittle.sudokusolver;
/*ww  w  .  j  ava  2  s. c o  m*/
public class Solve {

  public static boolean bruteForce() {
    //If all values found, exit loop
    if (gridFull()){
      return true;
    }
    
    //Find next spot to fill
    findNext();
    
    //Cycle number 1 through 9
    for(int n = 1; n <= 9; n++){
      if (noConflicts(n)){
        //Assign spot new number
        Grid.grid[Grid.row][Grid.col] = n;
        //Try new number
        if (bruteForce()){
          //Walk out of loop
          return true;
        }
        //Assignment did not work, reset
        Grid.grid[Grid.row][Grid.col] = 0;
        //Go back to old spot, try again
        backstep();
      }
    }
    return false;
  }

  //Go back to old spot
  private static void backstep() {
    if(Grid.col != 0){
      Grid.col -= 1;
    }
    else if (Grid.row != 0){
      Grid.col = 8;
      Grid.row -= 1;
    }
    
    //Pass over fixed values
    if(Grid.gridBool[Grid.row][Grid.col]){
      backstep();
    }
    
  }

  //Find next empty spot
  private static void findNext() {
    for(int i = 0; i < 9; i++){
      for( int j = 0; j < 9; j++){
        if(Grid.grid[i][j] == 0){
          //Assign location
          Grid.row = i;
          Grid.col = j;
          return;
        }
      }
    }
  }

  private static boolean gridFull() {

    for(int i = 0; i < 9; i++){
      for( int j = 0; j < 9; j++){
        if(Grid.grid[i][j] == 0){
          //Empty spot found
          return false;
        }
      }
    }
    //No empty spots found
    return true;
  }

  public static boolean noConflicts(int n) {
    //Check row, columns and sectors for conflicts
    if (rowGood(n) && colGood(n) && sectorGood(n)){
      return true;
    } else {
      return false;
    }
    
  }

  private static boolean rowGood(int n) {
    for(int j = 0; j < 9; j++){
      //Pass over current location
      if (j != Grid.col){
        if (Grid.grid[Grid.row][j] == n){
          //Conflict found
          return false;
        }
      }
    }
    return true;
  }

  private static boolean colGood(int n) {
    for(int i = 0; i < 9; i++){
      //Pass over current location
      if (i != Grid.row){
        if (Grid.grid[i][Grid.col] == n){
          //Conflict found
          return false;
        }
      }
    }
    return true;
  }
  
  private static boolean sectorGood(int n){
    int initI;
    int initJ;
    
    //Start in corner of current sector
    if(Grid.row < 3){
      initI = 0;
    } else if (Grid.row >= 6){
      initI = 6;
    } else {
      initI = 3;
    }
    
    if(Grid.col < 3){
      initJ = 0;
    } else if (Grid.col >= 6){
      initJ = 6;
    } else {
      initJ = 3;
    }
    
    for(int i = 0; i < 3; i++){
      for(int j = 0; j < 3; j++){
        //Pass over current location
        //Add offsets
        if (initI + i != Grid.row && initJ + j != Grid.col){
          //Add offsets
          if(Grid.grid[initI + i][initJ + j] == n){
            //Conflict found
            return false;
          }
        }
      }
    }
    return true;
  }
}

Java Source Code List

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