DATA-STRUCTURES-BASICS5 MIN READ
Design undo and redo with two stacks
Apply stack behavior to undo and redo state management.
The stale redo A user types A, types B, undoes B, then types C. The app still allows redo B, creating a branch that should no longer exist. The stack rule is what protects the user's timeline. Undo model Two stacks, one branch History is LIFO. Redo is the actions you just backed out of, until a new action changes the future. One list Actions plus index pointer Buttons follow state transitions instead of ad hoc indexes. A redo stack is valid only while the user stays on the same history branch. 01 Record 02 Undo 03 Branch Decision 1…
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