原题链接：https://leetcode.com/problems/lemonade-change/

bool lemonadeChange(vector<int>& bills) {
    int tens = 0, fives = 0;
    for (auto x : bills) {
        if (x == 5) {
            fives ++ ;
        } else if (x == 10) {
            if (fives) {
                fives -- ;
                tens ++ ;
            } else {
                return false;
            }
        } else if (x == 20) {
            int t = 15;
            if (tens) {
                tens -- ;
                t -= 10;
            }
            while (t && fives) {
                fives -- ;
                t -= 5;
            }
            if (t) {
                return false;
            }
        }
    }
    return true;
}