do you have to use arrays? I would use a hash and write something like that :

@bigram = ( 'aa' .. 'zz' );
@bigram_list = ("ac" , "ab" , "wd" , "xs" ); 
$bigram_str = join " " @bigram;
my %bigram_exist;

foreach $bigram_test (@bigram_list)
      { 
      if ( $bigram_str =~ m/$bigram_test/
           {
           $bigram_exist{$bigram_test}=1;
           }
      else 
           {
           $bigram_exist{$bigram_test} = 0;
           {
      }
[download]

If you really need an array, then change the foreach into a for

(...)
my @bigram_exist;

for (i=0 ; i<=@bigram_list ; i++) 
      {
      if ( $bigram_str =~ m/$bigram_list[i]/
           {
           $bigram_exist[i]= 1 ;
           }
      else 
           {
           $bigram_exist[i] = 0;
           {
      }
[download]

either way you'll obtain a hash or an array with as many keys/items as your list.