题目：

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代码(首刷自解 2024年2月15日）：

class Solution {
public:bool lemonadeChange(vector<int>& bills) {vector<int> leftchange(2,0);//leftchange[0]代表5元数量，1代表10for (int i = 0; i < bills.size(); ++i) {if (bills[i] == 5) leftchange[0]++;else if (bills[i] == 10) {leftchange[1]++;if (leftchange[0] == 0) return false;else leftchange[0]--;} else {//顾客付了20if (leftchange[1] > 0) {leftchange[1]--;if (leftchange[0] == 0) return false;else leftchange[0]--;} else {if (leftchange[0] < 3) return false;else leftchange[0] = leftchange[0] - 3;}}}return true;}
};