@a = qw(a a b b c c c d e e e e e f f)
 #   ix: 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1
 #       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
 #start: * - * - * - - * * - - - - * -
 @start = (0, 2, 4, 7, 8, 13);