How can the error be corrected?

int func $($int$[]$ arr, int size$)\{$

if $($size $==1$ && arr$[0]==1)\{$

return $0$; $\}$

return fun$($arr$,0,$ size $1)$;$\}$

public static int fun $($int$[]$ arr, int a$,$ int b$)\{$

int m;

if $($b $<$ a$)\{$

return $-1$; $\}$

mid $=($a $+$ b$)/2$;

if $(1==$ arr$[$m$]$ && $0==$ arr$[$m $1])\{$

return m; $\}$

if $(0==$ arr$[$m$])\{$

return fun$($arr$,$ m $+1,$ b$)$;

$\}$ else $\{$

return fun$($arr$,$ a$,$ m $1)$; $\}\}$

a$.$ Modify the method to return the index of the last $1.$

b$.$ No correction is needed.

c$.$ Do not sort the array.

d$.$ Change the condition to $1==$ arr$[$m$]$ && $($m$==0||0==$ arr$[$m$-1]).$