Core pattern
State Machine DP
Step 8 of 14Pattern 6 of 7
×How to recognize it fast
This is the pattern for timeline problems where the situation you are in today changes what you are allowed to do tomorrow.
When you see
buy / sell stockcooldowntransaction feelimited transactionsactions over time
Think
- What state am I in today?
- Am I holding, resting, cooling down, or spending one of a limited number of actions?
What to do once the pattern is clear
Core trick
- Track the situation, not just the profit.
- Each day transitions between a small number of valid states.
- Once the states are explicit, the recurrence is often very short.
Shortcut recognition
Yesterday changes todayHolding versus not holding mattersA finite set of action states over time
Hidden trick
Students often store only one running profit and lose the real constraint. State machine DP works because you model the mode you are currently in.
Typical stock states
holding, notHolding, cooldown, transactionsLeft