百马百担问题：有100匹马，驮100担货。大马驮3担，中马驮2担

function horseGoods($horse,$goods)
{
    $array = [];
    for ($a=0; $a <= ($horse/3); $a++) { 
        for ($b=0; $b < ($horse/2); $b++) { 
            $c = $horse - $a - $b ;
            if (3*$a + 2*$b + $c/2 == $goods) {
                    $array[] = [
                        'a'=>$a,
                        'b'=>$b,
                        'c'=>$c,
                    ];
            }
        }
    }
    return $array;
}