Leetcode 948. Bag of Tokens

Given tokens and initial power, you can either spend power to gain score by playing small tokens face-up or spend score to gain power by playing large tokens face-down; maximize final score by optimally trading power and score. This is typically solved with a greedy two-pointer strategy on the sorted tokens to decide when to take a low-cost token for +1 score or sacrifice a point to replenish power.