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Author: Chao Huang
Email:   [email protected]
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How to run:
This is a java code for Symantec interview
How to run:
./run.sh
The result hold in the result.txt

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Basic idea:
I define two classes here: vendor_item and vendor_machine
vendor_item is simple, just for some basic prosperity for the vendor

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Basic:
In order to save memory to the vendor machine, I just create the parameters for each item. 
If the program needs to output all the items, you can just call 'return VenderItem(name,price)' to create a new item and return.
So everything in this machine are just parameters.

Data flow:
Firstly, we create a machine as a singleton. So in the whole program, there will be just one machine.
Then, we update the machine using 'item.txt'
Then we make transactions using 'customers.txt'
The result will be shown in both console and 'result.txt'

Machine skills:
The machine has the following functions:
1. Check whether all the input will be correct
2. If the current coins is not enough to pay change to customers. Then it will stop
3. If the item is sold out, it will stop
4. The machine will try to give the change coins as less as it can

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Detail:
vendor_machine is quite complex.
vendor_machine:
    member (all private):
        _id2name: this is a hash table transform id to item name
        _name2id: this is a hash table transform name to id
        _item_count: this is a hash table. It tells the machine how many items are left in the machine for the item id
        _coin_count: this is a array. it tells the machine, how many coins are left for a specific coins. there are just three types coins: $5,$1,$0.25
        _item_price: this is just a hash table. When given a item id, we can know its price directly
        _size: how many item types for this machine, default is 100
        _revenue: what is the currently revenue for this machine
    Function:
        protected: returnCurrent(): return the current revenue
        protected: show_all_food(): show the current machine status
        protected: add_item(name, price): given a name and item price, put it into the machine.
                                    This action will update _item_count, _id2name, _id2price
        protected: transaction(id,price): do a transaction:
                                I make several results for this machine
                                    a. code input is error
                                    b. item is sold out
                                    c. input money is not enough to pay for this item
                                    d. machine's coins is not enough to pay for change
                                    e. user gives wrong coins to the vendor_machine