if a character of str2 is also present in str1 , then mark its presence as - 1
if ( present [ str2 [ i ] . charCodeAt ( 0 ) - ' ' . charCodeAt ( 0 ) ] == 1 || present [ str2 [ i ] . charCodeAt ( 0 ) - ' ' . charCodeAt ( 0 ) ] == - 1 ) present [ str2 [ i ] . charCodeAt ( 0 ) - ' ' . charCodeAt ( 0 ) ] = - 1 ;