#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

bool valid (const vector<int> & board, int maxcol)
{
    for (int i = 0; i < maxcol; i++)
    {
        for (int j = i+1; j < maxcol; j++)
        {
            if (board[i] == board[j])
                // rows collide --- queens under threat
            {
                return false;
            }
            if (j-i == abs(board[i]-board[j]))
                // diagonals collide --- queens under threat
            {
                return false;
            }
        }
    }
    return true;
}

bool solve_8queens (int column, vector<int> & board)
{
    if (column > 8)
    {
        return true;
            // we only call the next level if everything up to the
            // current level was fine --- if we call for column 9,
            // it means that we have our solution
    }
    for (int row = 0; row < 8; row++)
    {
        board[column] = row;
        if (valid(board, column))
        {
            if (solve_8queens (column+1, board))
            {
                return true;
            }
        }
    }
        // we completed the loop and nothing worked;  backtrack
        // and have the previous level keep trying
    return false;
}

int main()
{
    vector<int> board(8);

    if (solve_8queens(0, board))
    {
        for (int i = 0; i < 8; i++)
        {
            cout << board[i] << "   ";
        }
    }
    cout << endl;
}