N Queens Program in C++

nqueens.cc

#include "nqueens.h"
int main()
{
	int N;
	cout<<"Enter N value :";
	while(cin>>N)
	{
		solveNQueens(N);//function call for the solveNQueens function.
	}
	return(0);
}
/****************************************************************

   FUNCTION:   solveNqueens 

   ARGUMENTS:  const unsigned& n

   RETURNS:    Nothing

   NOTES:      This function first initiates the board with value false and then checks wheather the solution exists or not. 
****************************************************************/

void solveNQueens(const unsigned& n)
{
	vector<vector<bool>> board(n, vector<bool>(n));
	initBoard(board);//function call for the initBoard function
	srand(time(NULL));
	cout<<"Size of the chessboard :"<<board.size()<<" x "<<board.size()<<endl;
	if(solveNQueensUtil(board, 0, 0))//function call for the solveNQueensUtil function.
	{
		printBoard(board);//function call for the printBoard function.
	}
	else
	{
		cout<<"No solution exists "<<endl;
	}
}

/****************************************************************

   FUNCTION:   solveNQueensUtil 

   ARGUMENTS:  vector<vector<bool>>& board, const unsigned& row,unsigned int col.

   RETURNS:    boolean value i.e true or false

   NOTES:      This function places the queens in correct position if at all they exist.
****************************************************************/

bool solveNQueensUtil(vector<vector<bool>>& board, const unsigned& row, unsigned int col)
{
	if(row >= board.size())	return true;//If all queens have been successfully placed then return true.
	for(unsigned i=0;i<board.size();i++)
	{
		if(i == 0)
		{	
			if(isSafe(board, row, col))//function call for the isSafe function.
			{
				board[row][col] = true;
				col = RNG(0, board.size()-1);////function call for the RNG function.
				if(solveNQueensUtil(board, row+1, col))	
					return true;
				board[row][col] = false;//Backtracking if solution not found.
			}
		}
		if(i != col)
		{
			if(isSafe(board, row, i))
			{
				board[row][i] = true;
				col = RNG(0, board.size()-1);
				if(solveNQueensUtil(board, row+1, col)) 	
					return true;
				board[row][i] = false;
			}
		}
	}
	return false;
}	
/****************************************************************

   FUNCTION:   isSafe

   ARGUMENTS:  const vector<vector<bool>>& board, const int& row, const int& col

   RETURNS:    boolean value

   NOTES:      This function checks if the queen can be placed in that particular place or not.
****************************************************************/

bool isSafe(const vector<vector<bool>>& board, const int& row, const int& col)
{
	for(unsigned i=0;i<(unsigned)row;i++)
	{
	for(unsigned j=0;j<board.size();j++)
	{
		if(board[i][j] == true) 
		{
			if(abs(row-(int)i) == abs(col-(int)j))	
				return false;
		}
	}
	if(board[i][col] == true)	return false;
	}
	return true;
}
/****************************************************************

   FUNCTION:   printBoard

   ARGUMENTS:  const vector<vector<bool>>& board

   RETURNS:    None

   NOTES:      This function prints the 2D vector.
****************************************************************/

void printBoard(const vector<vector<bool>>& board)
{
	for(unsigned i=0;i<board.size();i++)
	{
	for(unsigned j=0;j<board.size();j++)
	{
		if(board[i][j] == true)
		{
			cout<<" Q ";
		}
			else	cout<<" . ";
	}
	cout<<endl;
	}
}
/****************************************************************

   FUNCTION:   RNG

   ARGUMENTS:  int low, int high

   RETURNS:    int

   NOTES:      This function generates a random number between to given values.
****************************************************************/
int RNG(int low, int high)
{
    int r=(rand()%(high-low+1))+low;
    return r;
}
/****************************************************************

   FUNCTION:   initBoard

   ARGUMENTS:  vector<vector<bool>>& board

   RETURNS:    None

   NOTES:      This function initiates the 2D vector.
****************************************************************/

void initBoard(vector<vector<bool>>& board)
{
	for(unsigned i=0;i<board.size();i++)
	{
		for(unsigned j=0;j<board.size();j++)
		{
			board[i][j] = false;
		}
	}
	
}

nqueens.h

#ifndef H_NQUEENS
#define H_NQUEENS
#include "/home/cs689/common/689.h"
#endif
bool solveNQueensUtil(vector<vector<bool>>& board, const unsigned& row, unsigned int col);
bool isSafe(const vector<vector<bool>>& board, const int& row, const int& col);
void solveNQueens(const unsigned& n);
void initBoard(vector<vector<bool>>& board);
void printBoard(const vector<vector<bool>>& board);
int RNG(int low, int high);