(Easy) Lemonade Change LeetCode

Description:

At a lemonade stand, each lemonade costs $5. 

Customers are standing in a queue to buy from you, and order one at a time (in the order specified by bills).

Each customer will only buy one lemonade and pay with either a $5, $10, or $20 bill.  You must provide the correct change to each customer, so that the net transaction is that the customer pays $5.

Note that you don't have any change in hand at first.

Return true if and only if you can provide every customer with correct change.

 

Example 1:

Input: [5,5,5,10,20]
Output: true
Explanation: 
From the first 3 customers, we collect three $5 bills in order.
From the fourth customer, we collect a $10 bill and give back a $5.
From the fifth customer, we give a $10 bill and a $5 bill.
Since all customers got correct change, we output true.

Example 2:

Input: [5,5,10]
Output: true

Example 3:

Input: [10,10]
Output: false

Example 4:

Input: [5,5,10,10,20]
Output: false
Explanation: 
From the first two customers in order, we collect two $5 bills.
For the next two customers in order, we collect a $10 bill and give back a $5 bill.
For the last customer, we can't give change of $15 back because we only have two $10 bills.
Since not every customer received correct change, the answer is false.

 

Note:

• 0 <= bills.length <= 10000
• bills[i] will be either 5, 10, or 20.

 

 

Solution:

class Solution {
    public boolean lemonadeChange(int[] bills) {
        
        Stack<Integer> five = new Stack<Integer> ();
        
        Stack<Integer> ten = new Stack<Integer> ();
        
        Stack<Integer> twenty = new Stack<Integer> ();
        
        
        for(int i = 0; i <bills.length ; i++){
            
            if(bills[i] ==5){
                
                five.push(5);    
            }
            
            else if(bills[i]==10){
                
                if(five.size()<1){
                    
                    return false;
                }
                else{
                    
                    five.pop();
                    
                    ten.push(10);
                }
            }
            
            else{
                
                if(five.size()<1){
                    return false;
                }
                
                else if( ten.size()<1&& five.size()<3){
                    return false;
                }
                
                else{
                    if(ten.size()>=1 ){
                        ten.pop();
                        
                        twenty.push(20);
                        
                        five.pop();
                    }
                    
                    else if(ten.size()<1){
                        
                        five.pop();
                        five.pop();
                        five.pop();
                        twenty.push(20);
                    }
                }
            }
            
            
        }
        
        return true;
    }
}