C++ Easy and Simple Explained Solution, O(n) - faster than 100%
\n// We just simulate the selling of lemonade.\nclass Solution {\npublic:\n    bool lemonadeChange(vector<int>& bills) {\n        int fives = 0, tens = 0;\n    
```\n// We just simulate the selling of lemonade.\nclass Solution {\npublic:\n    bool lemonadeChange(vector<int>& bills) {\n        int fives = 0, tens = 0;\n        for (auto bill : bills) {\n            \n            // first case - customer paid 5$ - no change needed\n            if (bill == 5) \n                fives++;\n            \n            // second case - customer paid 10$ - if we have a 5$ bill, give it. Otherwise - return false\n            else if (bill == 10) {\n                if (fives == 0) return false;\n                tens++;\n                fives--;\n            }\n            \n            // third case - customer paid 20$ - if we have 5$ and 10$ bills - give that.\n            // Else - if we have three 5$ bills - give that.\n            // Otherwise - return false.\n            else {\n                if (fives > 0 && tens > 0) {\n                    fives--;\n                    tens--;\n                }\n                else if (fives >= 3) fives -= 3;\n                else return false;\n            }\n        }\n        return true;\n    }\n};\n```\n**Like it? please upvote...**
['C']