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hanibhathanibhat
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adds blockchain implementation
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‎README.md‎

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@@ -69,6 +69,7 @@ Remember that each data has its own trade-offs. And you need to pay attention mo
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* `A` [Disjoint Set](src/data-structures/disjoint-set) - a union–find data structure or merge–find set
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* `A` [Bloom Filter](src/data-structures/bloom-filter)
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* `A` [LRU Cache](src/data-structures/lru-cache/) - Least Recently Used (LRU) cache
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* `A` [Blockchain](src/data-structures/blockchain/) - Blockchain
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## Algorithms
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‎src/data-structures/blockchain/Blockchain.js‎

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import Block from './BlockchainBlock';
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import BlockchainTransaction from './BlockchainTransaction';
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export default class Blockchain {
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/**
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* @param {number} [difficulty=2] The difficulty level for mining new blocks
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* Higher values require more computational work
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*/
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constructor(difficulty = 2) {
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this.difficulty = difficulty;
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/**
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* @type {Array<Block>}
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*/
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this.chain = [];
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/**
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* @type {Array<BlockchainTransaction>}
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*/
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this.pendingTransactions = [];
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/**
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* @type {number}
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*/
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this.minerReward = 10;
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/**
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* @type {Map<string, number>}
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*/
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this.balances = new Map();
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/**
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* @type {Map<string, Array<Object>>}
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*/
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this.transactionsByAddress = new Map();
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this.createGenesisBlock();
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}
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/**
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* Creates the first block in the chain.
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* @private
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*/
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createGenesisBlock() {
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const genesisBlock = new Block({
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index: 0,
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data: 'Genesis Block',
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previousHash: '0',
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});
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genesisBlock.mineBlock(this.difficulty);
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this.chain.push(genesisBlock);
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}
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/**
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* @returns {Block} The last block in the chain
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*/
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getLatestBlock() {
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return this.chain[this.chain.length - 1];
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}
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/**
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* @param {string} address The address whose balance should be adjusted
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* @param {number} amount The amount to add to the current balance
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*/
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updateBalance(address, amount) {
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this.balances.set(address, (this.balances.get(address) || 0) + amount);
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}
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/**
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* @param {number} blockIndex The index of the block that stores the transaction
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* @param {BlockchainTransaction} transaction The transaction to index
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*/
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indexTransaction(blockIndex, transaction) {
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const addresses = new Set([transaction.from, transaction.to]);
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for (const address of addresses) {
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const addressTransactions = this.transactionsByAddress.get(address) || [];
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addressTransactions.push({
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block: blockIndex,
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transaction,
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});
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this.transactionsByAddress.set(address, addressTransactions);
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}
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}
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/**
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* @param {BlockchainTransaction} transaction The transaction object to add
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* @returns {boolean} True if the transaction was added successfully
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*/
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addTransaction(transaction) {
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// Basic validation: in production, use more robust checks
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if (!transaction.from || !transaction.to || !transaction.amount) {
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return false;
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}
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if (transaction.amount <= 0) {
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// Invalid transaction: amount must be positive
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return false;
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}
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this.pendingTransactions.push(transaction);
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this.updateBalance(transaction.from, -transaction.amount);
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this.updateBalance(transaction.to, transaction.amount);
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return true;
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}
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/**
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* Mines pending transactions into a new block and rewards the miner.
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* This method creates a new block, mines it according to the difficulty level,
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* and adds it to the blockchain.
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*
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* @param {string} minerAddress - The address of the miner who will receive the reward
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* @returns {Block|null} The newly mined block, or null if no pending transactions exist
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*/
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minePendingTransactions(minerAddress) {
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// Add miner reward transaction
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const transaction = new BlockchainTransaction({
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from: 'System',
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to: minerAddress,
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amount: this.minerReward,
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description: 'Mining Reward',
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});
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this.pendingTransactions.push(transaction);
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this.updateBalance(transaction.from, -transaction.amount);
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this.updateBalance(transaction.to, transaction.amount);
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// Create new block with pending transactions
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const newBlock = new Block({
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index: this.chain.length,
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data: this.pendingTransactions,
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previousHash: this.getLatestBlock().hash,
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});
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// Mine the block
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newBlock.mineBlock(this.difficulty);
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// Add to chain
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this.chain.push(newBlock);
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for (const transaction of newBlock.data) {
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this.indexTransaction(newBlock.index, transaction);
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}
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// Clear pending transactions
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this.pendingTransactions = [];
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return newBlock;
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}
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/**
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* Validates the entire blockchain by checking:
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* 1. Each block's hash is correctly calculated
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* 2. Each block's previous hash matches the previous block's hash
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* 3. No blocks have been tampered with
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*
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* @returns {boolean} True if the blockchain is valid, false otherwise
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*/
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isChainValid() {
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if (this.chain.length <= 1) {
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// An empty chain or a chain with only the genesis block is considered valid
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return true;
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}
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// Check each block starting from the second block (index 1)
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for (let i = 1; i < this.chain.length; i++) {
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const currentBlock = this.chain[i];
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const previousBlock = this.chain[i - 1];
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// Verify current block's hash is correct
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if (currentBlock.hash !== currentBlock.calculateHash()) {
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// The block has been tampered with
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return false;
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}
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// Verify link to previous block
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if (currentBlock.previousHash !== previousBlock.hash) {
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// The link to the previous block is invalid
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return false;
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}
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}
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return true;
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}
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/**
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* @param {string} address The address to check balance for
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* @returns {number} The total balance of the address
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*/
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getBalance(address) {
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return this.balances.get(address) || 0;
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}
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/**
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* @param {string} address The address to find transactions for
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* @returns {Array<Object>} An array of transaction objects involving the address
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*/
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getTransactionsForAddress(address) {
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return (this.transactionsByAddress.get(address) || []).slice();
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}
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}

‎src/data-structures/blockchain/BlockchainBlock.js‎

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import crypto from 'crypto';
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export default class Block {
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/**
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* @param {Object} blockParams - The block parameters
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* @param {number} blockParams.index - The position of the block in the blockchain
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* @param {string} [blockParams.timestamp] - The creation time of the block in ISO format
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* @param {Array|String} blockParams.data - The transaction data stored in this block
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* @param {string} blockParams.previousHash - The hash of the previous block in the chain
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* @param {number} [blockParams.nonce=0] - The number used once for proof of work calculations
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*/
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constructor({
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index,
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timestamp = new Date().toISOString(),
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data,
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previousHash,
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nonce = 0,
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}) {
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this.index = index;
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this.timestamp = timestamp;
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this.data = data;
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this.previousHash = previousHash;
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this.nonce = nonce;
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this.hash = this.calculateHash();
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}
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/**
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* @private
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* @returns {string} The hexadecimal representation of the block's hash
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*/
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calculateHash() {
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const blockData = JSON.stringify({
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index: this.index,
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timestamp: this.timestamp,
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data: this.data,
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previousHash: this.previousHash,
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nonce: this.nonce,
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});
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return crypto.createHash('sha256').update(blockData).digest('hex');
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}
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/**
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* @param {number} difficulty - The number of leading zeros required in the hash
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*/
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mineBlock(difficulty) {
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const target = '0'.repeat(difficulty);
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while (this.hash.substring(0, difficulty) !== target) {
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this.nonce += 1;
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this.hash = this.calculateHash();
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}
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}
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}

‎src/data-structures/blockchain/BlockchainTransaction.js‎

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export default class BlockchainTransaction {
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/**
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* @param {Object} transactionParams - The transaction parameters
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* @param {string} transactionParams.from - The sender's address
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* @param {string} transactionParams.to - The recipient's address
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* @param {number} transactionParams.amount - The transaction amount
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* @param {string} [transactionParams.description=''] - Optional description of the transaction
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*/
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constructor({
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from,
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to,
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amount,
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description = '',
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}) {
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this.from = from;
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this.to = to;
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this.amount = amount;
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this.description = description;
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}
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}

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