efficient traversal changelist

i have list changes list - adds deletes. list vast - contend 10'000 items.

i wish know state list after change 9'000.

i transport list start proceed change 9'000. seems bit extensively me.

i keep list equipment record they're total they're deleted, following transport list list during sole change. adds deletes equally likely, i separate array list elements i need transport through...

but large o footnote says halving distance problem doesn't things some-more fit (if i've supposed correctly).

i cache state list during each 100th 1000th change... nonetheless again, large o says dividing array equipment 'n' doesn't things some-more efficient.

so fit proceed doing this? there an fit proceed doing this?

more details:
specifically, i'm tracking memory allocations / deallocations tradition allocater. any allocation / deallocation an eventuality list. any allocation unparalleled id. i'd know now allocated after (e.g) 9'000 events.

my initial thought store, any id, eventuality allocated eventuality deallocated. following transport list adult initial allocation whose alloc eventuality incomparable 9000. nonetheless i said, wholly separate array equipment i'd need transport through.

i indicate finished mike f - walking nearest 100th vigilant consistent time...