Consider the following stack:

$+----+$

$|16|<-$ top

$+----+$

$|20|$

$+----+$

$|12|$

$+----+$

$|19|<-$ bottom

$+----+$

Of the functions below, which ones return a stack whose contents match the stack depicted above?

There might be more than one correct answer. Be sure to select all that apply.

functionA$()$

Stack functionA$()$

$\{$

Stack s;

s$.$push$(16)$;

s$.$push$(20)$;

s$.$push$(12)$;

s$.$push$(19)$;

return s;

$\}$

functionB$()$

$//$ Note: This function is identical to functionA$(),$ except the

$//$ initial four values are pushed in a different order.

Stack functionB$()$

$\{$

Stack s;

s$.$push$(19)$;

s$.$push$(12)$;

s$.$push$(20)$;

s$.$push$(16)$;

return s;

$\}$

functionC$()$

Stack functionC$()$

$\{$

Stack s;

s$.$push$(16)$;

s$.$push$(20)$;

s$.$push$(12)$;

s$.$push$(19)$;

s$.$peek$()$;

s$.$peek$()$;

s$.$peek$()$;

s$.$peek$()$;

return s;

$\}$

functionD$()$

$//$ Note: This function is identical to functionC$(),$ except the

$//$ initial four values are pushed in a different order.

Stack functionD$()$

$\{$

Stack s;

s$.$push$(19)$;

s$.$push$(12)$;

s$.$push$(20)$;

s$.$push$(16)$;

s$.$peek$()$;

s$.$peek$()$;

s$.$peek$()$;

s$.$peek$()$;

return s;

$\}$

functionE$()$

Stack functionE$()$

$\{$

Stack s;

s$.$push$(16)$;

s$.$push$(20)$;

s$.$push$(12)$;

s$.$push$(19)$;

s$.$pop$()$;

s$.$pop$()$;

s$.$pop$()$;

s$.$pop$()$;

return s;

$\}$

functionF$()$

$//$ Note: This function is identical to functionE$(),$ except the

$//$ initial four values are pushed in a different order.

Stack functionF$()$

$\{$

Stack s;

s$.$push$(19)$;

s$.$push$(12)$;

s$.$push$(20)$;

s$.$push$(16)$;

s$.$pop$()$;

s$.$pop$()$;

s$.$pop$()$;

s$.$pop$()$;

return s;

$\}$

functionG$()$

Stack functionG$()$

$\{$

Stack s;

s$.$push$(16)$;

s$.$push$(20)$;

s$.$push$(12)$;

s$.$push$(19)$;

$//$ The return value from s$.$peek$()$ is pushed onto s$.$

s$.$push$($s$.$peek$())$;

return s;

$\}$

functionH$()$

$//$ Note: This function is identical to functionG$(),$ except the

$//$ initial four values are pushed in a different order.

Stack functionH$()$

$\{$

Stack s;

s$.$push$(19)$;

s$.$push$(12)$;

s$.$push$(20)$;

s$.$push$(16)$;

$//$ The return value from s$.$peek$()$ is pushed onto s$.$

s$.$push$($s$.$peek$())$;

return s;

$\}$

functionI$()$

Stack functionI$()$

$\{$

Stack s;

s$.$push$(16)$;

s$.$push$(20)$;

s$.$push$(12)$;

s$.$push$(19)$;

$//$ The return value from s$.$pop$()$ is pushed onto s$.$

s$.$push$($s$.$pop$())$;

return s;

$\}$

functionJ$()$

$//$ Note: This function is identical to functionI$(),$ except the

$//$ initial four values are pushed in a different order.

Stack functionJ$()$

$\{$

Stack s;

s$.$push$(19)$;

s$.$push$(12)$;

s$.$push$(20)$;

s$.$push$(16)$;

$//$ The return value from s$.$pop$()$ is pushed onto s$.$

s$.$push$($s$.$pop$())$;

return s;

$\}$

functionK$()$

Stack functionK$()$

$\{$

Stack s$1$;

Stack s$2$;

s$1.$push$(16)$;

s$1.$push$(20)$;

s$1.$push$(12)$;

s$1.$push$(19)$;

while $(!$s$1.$isEmpty$())$

$\{$

$//$ Pop value from s$1$ and push it onto s$2.$

s$2.$push$($s$1.$pop$())$;

$\}$

return s$2$;

$\}$

functionL$()$

$//$ Note: This function is identical to functionK$(),$ except the

$//$ initial four values are pushed in a different order.

Stack functionL$()$

$\{$

Stack s$1$;

Stack s$2$;

s$1.$push$(19)$;

s$1.$push$(12)$;

s$1.$push$(20)$;

s$1.$push$(16)$;

while $(!$s$1.$isEmpty$())$

$\{$

$//$ Pop value from s$1$ and push it onto s$2.$

s$2.$push$($s$1.$pop$())$;

$\}$

return s$2$;

$\}$