how does bitcoin prevent double-spending

Question

can someone help me create a Pseudocode that shows how bitcoin prevents double-spending? here is my code

This program is to prevent double-spending: Person A and Person B go to a store with only one collective BTC to spend. Person A buys a TV costing exactly 1 BTC. Person B buys a motorcycle that also costs exactly 1 BTC.

blockchain = [] pool_of_unconfirmed_transactions = [] Both transactions go into a pool of unconfirmed transactions: pool_of_unconfirmed_transactions.append(person A buys) pool_of_unconfirmed_transactions.append(person B buys) only the first transaction gets confirmations and is verified by miners in the next block. If person A buys == first buyer: person A's transaction == valid blockchain.append(person A's transaction) del mem_pool[person B's transaction] else: person B's transaction == valid del mem_pool[person A's transaction]

Whichever transaction gets the maximum number of network confirmations (typically a minimum of six) will be included in the blockchain, while others are discarded. Once confirmations and transactions are put on the blockchain they are time-stamped, rendering them irreversible and impossible to alter.

Is it ok? any suggestion?