860. Lemonade Change

 1 class Solution 
 2 {
 3 public:
 4     bool lemonadeChange(vector<int>& bills) 
 5     {
 6         int five = 0, ten = 0;
 7         for (int i : bills) 
 8         {
 9             if (i == 5) five++;
10             else if (i == 10) five--, ten++;
11             else if (ten > 0) ten--, five--;
12             else five -= 3;
13             if (five < 0) return false;
14         }
15         return true;
16     }
17 };

扫描一遍，问题不大