PHP: Dynamic Fibonnaci O(n)

dynamic_fibonnaci.php

<?php

// O(n) time complexity with constant space complexity
function fibonacci_dynamic($n){

    if($n == 0){
        return 0;
    }elseif($n == 1 OR $n == 2){
        return 1;
    }

    $fib[0] = 0;
    $fib[1] = 1;

    for($i=2; $i<=$n; $i++){
        $current_fib = $fib[0] + $fib[1];
        $fib[0] = $fib[1];
        $fib[1] = $current_fib;
    }

    return $fib[1];

}

var_dump(fibonacci_dynamic(10));