Partially retroactive: updates in the past and present, (fast) queries in the present

Fully retroactive: updates in the past and present, (fast) queries in the past and present

Easy general transformation: rollback

Weight-balanced B-trees (Arge and Vitter 2003, Bender et al. 2005)

Scapegoat trees (Galperin and Rivest 1993)

Various BST augmentations (prefix sum, etc.)

My implementation is mostly augmented scapegoat trees.

Related partially retroactive data structures

Fully retroactive priority queues—all the way

Performance improvements

Generalization

retroactive, a popular 6.851 final project by Chelsea Voss

rpqvis, a visualization project from this iteration of 6.851

retroactive-priority-queue, a similar implementation project from this iteration of 6.851 with different underlying data structures (treaps)