/*
* File: main.cpp
* Author:
*
* Develop and implement a stack-based Sudoku puzzle solver.
*
* When solved, each row must have all of the integers 1 – 9,
* each column must have all of the integers 1 – 9 and
* each of the nine 3-by-3 blocks must have all of the integers 1 – 9.
*
*/

#include <cstdlib>
#include <iostream>
#include <stack>
#include <fstream>
#include <iomanip>
using namespace std;

const short int BOARD_SIZE = 9;
const short int BLOCK_SIZE = 3;
const short int EMPTY_CELL = 0;
const int UNFILLED_INDEX = 15;
const int DIGIT_NUM = 9;
const short int MASK_0_CHOICE = 0xE1FF; // 1110000111111111
const short int MASK_ALL = 0xFFFF; // 1111111111111111
const short int MASK_0_CHOICE_TOGGLE = ~MASK_0_CHOICE; // 0001111000000000
const short int MASK_000F = 0x000F; // 0000000000001111
const short int MASK_ALL_AS_VALID_CHOICE = 0x01FF; // 0000000111111111

/**
* update 4 bits of current choice
* @param val the short int value
* @param currentChoice the choice to be filled in
* @return the updated value
*/
short int setChoice(short int val, int currentChoice);

/**
* get current choice from the short int value
* @param val the value
* @return the choice
*/
short int getChoice(short int val);

/**
* read data from cin
* @param board 2d array of number
*/
void readData(short int board[BOARD_SIZE][BOARD_SIZE], fstream & fin);

/**
* read date from an input stream
* for debugging
* @param board 2d array of number
* @param fin input stream
*/
void readData(short int board[BOARD_SIZE][BOARD_SIZE]);

/**
* print formated result to screen
* @param board 2 d array of numbers
*/
void printResult(short int board[BOARD_SIZE][BOARD_SIZE]);

/**
* print simple table
* for input data printing
* @param board 2d array of number
*/
void printData(short int board[BOARD_SIZE][BOARD_SIZE]);

/**
* print hex value of all filled cells for debugging
* @param board 2d array of number
*/
void printHex(short int board[BOARD_SIZE][BOARD_SIZE]);

/**
* print hex value of all cella for debugging
* @param board 2d array of number
*/
void printHexAll(short int board[BOARD_SIZE][BOARD_SIZE]);

/**
* set a bit to 0
* @param val the number
* @param position the position for setting
* @return a new value
*/
short int unsetNBit(short int val, int position);

/**
* set a bit to 1
* @param val the number
* @param position the position for setting
* @return a new value
*/
short int setNBit(short int val, int position);

/**
* count the number of valid choice in 9 first digits
* @param val the short int value
* @return number of valid choices
*/
int validChoiceCounter(short int val);

/**
* Preconditions bord contains an unsolved Sudoku puzzle
* Postconditions the best location is pushed onto the stack
* the best location is marked as filled in
* @param board 2d array of number
* @param st stack of indices of best cells
*/
bool findBest(short int board[BOARD_SIZE][BOARD_SIZE], stack<int> & st);

/**
* get the next valid choice
* @param val a short int number
* @return index of selected digit
*/
int getValidChoice(short int val);

/**
* Preconditions bord contains an unsolved Sudoku puzzle
* Postconditions bord contains a solved Sudoku puzzle
* @param board 2d aray of number
* @return true when the board is solved
*/
bool solve(short int board[BOARD_SIZE][BOARD_SIZE]);

int main(int argc, char** argv) {
/**
* Read the data from cin. Input consists of nine lines of
* nine characters. If a cell is filled in, its
* character will be a digit 1 – 9. If it is blank,
* its character is a period.
*/
/*
* Pro tip: You only need a single char variable for
* the input; no strings necessary.
*/
short int board[BOARD_SIZE][BOARD_SIZE];
readData(board);
//printData(board);
if (solve(board)) {
printResult(board);
}

return 0;
}

/**
* Preconditions bord contains an unsolved Sudoku puzzle
* Postconditions bord contains a solved Sudoku puzzle
* @param board 2d aray of number
* @return true when the board is solved
*/
bool solve(short int board[BOARD_SIZE][BOARD_SIZE]) {
// 2: Select the best empty cell and place its location on the stack
stack<int> st;
// printHexAll(board);
// cout << "******************\n";
findBest(board, st);
// printHexAll(board);
// cout <<"--------------------------------\n";
int i, j;
int top;
int validChoice;

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