Super Easy  Solution - O(n) TC, O(1) SC
Intuition\n Describe your first thoughts on how to solve this problem. \n\n# Approach\n Describe your approach to solving the problem. \n\n# Complexity\n- Time 
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->\n\n# Approach\n<!-- Describe your approach to solving the problem. -->\n\n# Complexity\n- Time complexity:O(n)\n<!-- Add your time complexity here, e.g. $$O(n)$$ -->\n\n- Space complexity:(1)\n<!-- Add your space complexity here, e.g. $$O(n)$$ -->\n\n# Code\n```\nclass Solution {\npublic:\n    bool lemonadeChange(vector<int>& bills) {\n       // 0th index -> 5 rs, 1st index-> 10rs, 2nd index->20 rs\n        vector<int> v = {0,0,0};\n\n        int i=0;\n        while(i<bills.size()){\n            // if 5 rs ka note hai \n            if(bills[i]==5){\n                v[0]++;\n            }\n            else if(bills[i]==10){\n                v[1]++;\n                // 5 rs ka change dena pdega\n                if(v[0]==0) return false;\n                else v[0]--;\n            }\n            else if(bills[i]==20){\n                v[2]++;\n                // 15 ka change dena hai\n                // ya toh ek 10 ka note and ek 5 ka note\n                if(v[1]>0 and v[0]>0){\n                    v[1]--;\n                    v[0]--;\n                }\n                // ya 5 ke 3 notes se 15 ka change denge\n                else if(v[0]>=3){\n                    v[0] = v[0] - 3;\n                }\n                // ni hai possible toh false\n                else return false;\n            }\n            i++;\n        }\n        return true;\n    }\n};\n```\nIf you like my soln please upvote this .\n![images.jpg](https://assets.leetcode.com/users/images/b01c2010-351a-4fa2-a083-33a46f195a52_1702130042.2643633.jpeg)\n\n\n
['C++']