Code Golf: Finite-state machine!

Answer 1

bash - 186 185 184 chars

declare -A a
read s x
while read f m t&&[ $m ];do a[$f $m]=$t;done
for((i=0;i-${#f};i++))do b="$s ${f:i:1}";s=${a[$b]};echo $b -\> $s;done
[ "$s" = "${s,}" ]&&echo REJECT||echo ACCEPT

Note that this does actually require bash - POSIX sh doesn't have associative arrays or the C-style for syntax (and probably doesn't have all the parameter expansions used either, although I haven't checked).

Edit: alternatively, for the exact same length,

declare -A a
read s x
while read f m t&&[ $m ];do a[$f $m]=$t;done
while [ $f ];do b="$s ${f:i:1}";f=${f:1};s=${a[$b]};echo $b -\> $s;done
[ "$s" = "${s,}" ]&&echo REJECT||echo ACCEPT