948. Bag of Tokens

class Solution:
    def bagOfTokensScore(self, tokens: List[int], P: int) -> int:
    # time O(NlgN) space O(N)
        # main idea: sort , then buy at the cheapest and sell at the most expensive using queue
        tokens.sort()
        q = collections.deque(tokens)
        cur = 0
        res = 0
        # continue condition: when there is non-zero current score or  there is enough buying power 
        while q and (q[0] <= P or cur):
            if q[0] <= P :
                P -= q.popleft()
                cur += 1
            else:
                P += q.pop()
                cur -= 1
            res = max(cur,res)
        return res