For the following operations, define the worst$-$case runtime complexity in big$-$O notation in terms of n$.$

int sum$1=0$;

int sum $=0$;

for $($int i $=1$; i $<=$ n; i$++)$

for $($int j $=1$; j $<=$ n; j$+=2)$

sum $+=($i$+$j$)$;

for $($int i $=1$; i $<=$ n; i$++)$

for $($int j $=1$; j $<=$ n; j$+=2)$

sum $+=($i$+$j$)$;

is it O$($n$^2),$ O$($n$^3),$ O$($n$),$ O$($log n$*$n$)$