8 Queens, problem with searching 2D array

Quote:

---

Originally Posted by vart

bool isPathViable(int row, int column)

is called AFTER the Queen is placed in the (row,column)

if(board[row][i]==1) for i == column will be ALWAYS true

so

Code:

---

void solve(int n,int row, int column)
{
    if(isPathViable(row,column))
  {
        addQueen(row,column);
        if(column == 8)
            displayBoard();
        else
            for(int i=0; i < n; ++i)
                solve(n,i,column+1);
        removeQueen(row,column);
  }
}

---

so,ething like that maybe?

---

I seem to get the same results with this, as I do with my code, just a blank board. Perhaps it is the loop in the main function that is messing me up?

EDIT- I've changed the loop in main, and I get queens that are placed, but they are kind of random, and don't follow the rules.

I've fixed it up a lot more. I got it to place the first queen in the top-left corner, then place the second queen in a way that it is safe from the first. However, after this, it doesn't go on to the other columns.

Main:

Code:

---

int main()
{
        int n=8;

        resetBoard();
       
        for(int i=0;i < 8;i++)
                solve(8,0,i);

        displayBoard();

        return 0;
}

---

Solve:

Code:

---

void solve(int n,int row, int column)
{
        if(isPathSuccess(row,column))
                displayBoard();
       
        else if(isPathViable(row,column))
        {
                addQueen(row,column);
               
                cout << "[" << row << "," << column << "]" << endl;
               
                for(int i=0; i < n; ++i)
                        solve(n,i,column+1);
        }
       
        else
                removeQueen(row,column);       
       
}

---

why do you remove the Queen from the cell where you have not placed it?

Quote:

---

Originally Posted by vart

why do you remove the Queen from the cell where you have not placed it?

---

I'm not sure that's the part I need help with. How would I remove the Queen that I placed, but that is in a threatening position?

I'm not really sure where to place the removeQueens function, and what to pass it, I've tried putting it everywhere it seems.

Code:

---

#include <iostream>

using namespace std;


void displayBoard(int size);
void addQueen(int row, int column);
void removeQueen(int row,int column);
void solve(int size, int column, int row);

bool isPathViable(int row, int column);

const int size = 8;
int board[size][size] = {0};


int main()
{
        for(int i=0;i < size;i++)
                solve(size,i,0);

        return 0;
}

void solve(int size,int row, int column)
{

        if(isPathViable(row,column))
        {
                addQueen(row,column);

                if(column == size - 1)
                {
                        displayBoard(size);
                }
                else
                {
                        for(int i=0; i < size; ++i)
                        {
                                if(i != row)
                                        solve(size,i,column+1);
                        }
                }
                removeQueen(row,column);       
        }
        return ;
}

bool isPathViable(int row, int column)
{
        for(int i=column-1;i >= 0; --i)        //Checks row
        {
                if(board[row][i]==1)
                        return false;

        }

        for(int j=row-1, k=column-1 ; j >= 0, k >= 0;--j, --k)        //Checks left and up diagonal
        {
                if(board[j][k]==1)
                        return false;

        }

        for(int u=row+1, h=column-1 ;u >= 0,h >= 0;++u,--h)        //Checks left and down diagonal
        {
                if(board[u][h]==1)
                        return false;
        }

        return true;

}

void displayBoard(int size)
{
        for(int i=0; i < size; ++i)
        {
                for(int j=0; j < size; ++j)
                        cout << board[i][j] << " ";

                cout << "\n";
        }
        cout << "\n";
        cout << "\n";
}

void addQueen(int row,int column)
{
        board[row][column]=1;
}

void removeQueen(int row,int column)
{
        board[row][column]=0;
}

---

find n differencies...

Thanks! It seems so simple, but I see what I messed up. I've been going crazy trying to figure this out! :D