The Big O notation is used in computer science to determine the runtime in certain scenarios. Determine the worst$-$case runtime for the following sorting algorithm written in pseudo code:

$1$ sort $($array a$)\{$

$2$ for $($n$=$a$.$size; n$>1$; $--$n$)\{$

$3$ for $($i$=0$; i a$[$i$+1])\{$

$5$ a$.$swap$($i$,$ i$+1)$

$6\}$

$7\}$

$8\}$

$9\}$