Problem - Bag of Tokens

You have tokens with values and start with power $P$ and score $0$.

You can play token $i$ face-up (lose $tokens[i]$ power, gain $1$ score) if you have enough power. Or play face-down (gain $tokens[i]$ power, lose $1$ score) if score $> 0$. Maximize final score.

Think about when to spend power and when to cash in score for power. Tricky: playing face-down gives you power but costs score.

You only do this when you cannot afford any face-up plays. The two-pointer setup ensures you always have access to both the smallest (cheapest to play face-up) and largest (best power gain face-down) tokens.