starting 0 letter a
length 0 new a start of new 
mid a
starting 1 letter b
length 1 new b start of new a
it 1
mid bab
starting 2 letter c
length 3 new c start of new bab
it 1
it 2
it 3
mid cbcacbc
starting 3 letter d
length 7 new d start of new cbcacbc
it 1
it 2
it 3
it 4
it 5
it 6
it 7
mid dcdbdcdadcdbdcd
dcdbdcdadcdbdcd