$delim = 'A -3 C -4 B';
$array = 
     ['A -4 A','A -1 C','C -4 D','D -4 B','B -3 C','C -2 B','B -1 E'];
            +   *    +   *    +   *    +   *    +   *    +   *

# Note that in $array,  starting from 
# second element $array->[1] until $array->[-1], 
# the first alphabet  ( asterisks *)  is  actually 
# a repeat of the last alphabet ( plus +) 
# from the previous element.