<?php
// eight-queens
// Author: Hannes du Plooy 
// Date: 20 Sep 2016      
// Objective: To solve the following
// Search for a chess board solution with 8 queens and no one
// endangering any other.
$board = array(0,0,0,0,0,0,0,0);

function EightQueens($line) {
    global $board;
    if ($line > 7) {
        return true;
    }
    for($column=0;$column<8;$column++) {
        $endangered = false;
        for($line2=0;$line2<$line;$line2++) {
            if ($board[$line2] == $column || abs($line-$line2) == abs($column-$board[$line2])) {
                $endangered = true;
                break;
            }
        }
        if (!$endangered) {
            $board[$line] = $column;
            if (EightQueens($line+1)) {
                return true;
            }
        }
    }
    return false;
}

if (EightQueens(0)) {
    for($i=0;$i<8;$i++) {
        for($j=0;$j<8;$j++) {
            if ($board[$i] == $j) {
                echo "Q";
            } else {
                echo ".";
            }
        }
        echo "\n";
    }
}