UNSW ProgComp: Problem 4 - 2008

<?php

$input = <<<END
7664 71994 9096 71785 26 904 668944 78 46 3869 64043
927 97 45923 49 790 360 29986 618 832040 30 77419
27 529 456 268052 5279 3832 28 67 23396 70500 3876
57 883 27 73734 924 144 6164 221 307 41 6753 75584
27191 61 3413 12 255255 5750 5104 99 3146 316 972 90
1069 8050 3472 60119 49 984 150910 48165 52829 3513
28 408 121393 21076 69218 678 877820 20348 7866 938
37 159 75534 81163 743219 74670 0
END;

function is_fibonacci($n){
    $x = 1;
    $y = 1;
    while($x < $n){
        $temp = $y;
        $y = $y + $x;
        $x = $temp;
    }
    return ($x == $n) ? true : false;
}

function is_triangle($n){
    $x = 1;
    $y = 1;
    while($x < $n){
        $x += $y+1;
        $y++;
    }
    return ($x == $n) ? true : false;
}

function is_even($n){
    if($n == 0){
        return false;
    }
    return ($n%2 == 0) ? true : false;
}

$input = preg_replace("#([ \n\r])+#", ' ', $input);
$input = explode(" ", $input);

//categorise numbers
$fib = array();
$evens = array();
$triangles = array();

foreach($input as $key => $value){
    if(is_fibonacci($value)){
        $fib[] = $value;
    }
    if(is_even($value)){
        $evens[] = $value;
    }
    if(is_triangle($value)){
        $triangles[] = $value;
    }
}

sort($fib);
sort($evens);
sort($triangles);

if(empty($fib)){
    $fib[] = "None";
}
if(empty($triangles)){
    $triangles[] = "None";
}
if(empty($evens)){
    $evens[] = "None";
}

echo "Even numbers:         min ".str_pad($evens[0], 5, ' ', STR_PAD_RIGHT)." max ".end($evens)."\n";
echo "Triangular numbers:   min ".str_pad($triangles[0], 5, ' ', STR_PAD_RIGHT)." max ".end($triangles)."\n";
echo "Fibonacci numbers:    min ".str_pad($fib[0], 5, ' ', STR_PAD_RIGHT)." max ".end($fib)."\n";