860. Lemonade Change

https://leetcode.com/problems/lemonade-change/

/*
    greedy algo, 
    
    becasue if we have $10, we use combination of $5 & $10 first

    time complexity: O(n) , space complecity: O(1)
*/    
class Solution {
    public boolean lemonadeChange(int[] bills) {
        int five = 0;
        int ten = 0;
        
        for (int bill : bills) {
            
            if (bill == 5) {
                five++; //$5 number ++
            } else if (bill == 10) { //$10 number ++, and changing $5 back
                five--;
                ten++;
                
            } else if (ten > 0) { // 20 dollars case, if we have ten coins, use combination of $5 & $10 first 
                five--;
                ten--;
                
            } else {
                five -= 3; //not enough $10, so using 3 $5 
            }
            
            if (five < 0) return false; // in loop, we found not enough change
        }
        return true;
    }
}