nqueen.cpp

#include<iostream>

using namespace std;

int col[20];

//Returns absolute value
int abs(int a)
{    return a < 0 ? -a : a;    }

//Prints col array
void print_col(int N)
{
    for(int i = 0; i < N; ++i)
        cout<<col[i]<<"   ";

    cout<<"\n";
}

//Checks if queen can be placed in row 'r' and column 'c'
int place(int r, int c)    
{
    for(int i = 0; i < r; ++i)
        if( (col[i] == c)                            //Same column
            || (abs(col[i]-c) == abs(i-r)) )        //Same diagonal
            return 0;

    return 1;
}

//Check for queen's placement starting at the kth row
void nq(int N, int k)
{
    //For each column
    for(int i = 0; i < N; ++i)
        //Can be placed at row k, col i
        if(place(k, i))
        {
            col[k] = i;

            //Reached last row successfully
            if(k == N-1) 
                print_col(N);

            //Check the next row
            else    
                nq(N, k+1);
        }
}

int main()
{
    //4x4 board. Start with row 0
    nq(4, 0);

    return 0;
}