Add prompt and solution for LC 2043. Simple Bank System

Author: timothyshores

2043. Simple Bank System.js

@@ -0,0 +1,80 @@
+/*
+
+2043. Simple Bank System
+
+You have been tasked with writing a program for a popular bank that will automate all its incoming transactions (transfer, deposit, and withdraw). The bank has n accounts numbered from 1 to n. The initial balance of each account is stored in a 0-indexed integer array balance, with the (i + 1)th account having an initial balance of balance[i].
+
+Execute all the valid transactions. A transaction is valid if:
+
+The given account number(s) are between 1 and n, and
+The amount of money withdrawn or transferred from is less than or equal to the balance of the account.
+Implement the Bank class:
+
+Bank(long[] balance) Initializes the object with the 0-indexed integer array balance.
+boolean transfer(int account1, int account2, long money) Transfers money dollars from the account numbered account1 to the account numbered account2. Return true if the transaction was successful, false otherwise.
+boolean deposit(int account, long money) Deposit money dollars into the account numbered account. Return true if the transaction was successful, false otherwise.
+boolean withdraw(int account, long money) Withdraw money dollars from the account numbered account. Return true if the transaction was successful, false otherwise.
+ 
+
+Example 1:
+
+Input
+["Bank", "withdraw", "transfer", "deposit", "transfer", "withdraw"]
+[[[10, 100, 20, 50, 30]], [3, 10], [5, 1, 20], [5, 20], [3, 4, 15], [10, 50]]
+Output
+[null, true, true, true, false, false]
+
+Explanation
+Bank bank = new Bank([10, 100, 20, 50, 30]);
+bank.withdraw(3, 10);    // return true, account 3 has a balance of $20, so it is valid to withdraw $10.
+                         // Account 3 has $20 - $10 = $10.
+bank.transfer(5, 1, 20); // return true, account 5 has a balance of $30, so it is valid to transfer $20.
+                         // Account 5 has $30 - $20 = $10, and account 1 has $10 + $20 = $30.
+bank.deposit(5, 20);     // return true, it is valid to deposit $20 to account 5.
+                         // Account 5 has $10 + $20 = $30.
+bank.transfer(3, 4, 15); // return false, the current balance of account 3 is $10,
+                         // so it is invalid to transfer $15 from it.
+bank.withdraw(10, 50);   // return false, it is invalid because account 10 does not exist.
+ 
+
+Constraints:
+n == balance.length
+1 <= n, account, account1, account2 <= 105
+0 <= balance[i], money <= 1012
+At most 104 calls will be made to each function transfer, deposit, withdraw.
+
+*/
+
+class Bank {
+  constructor(balances) {
+    this.balances = balances;
+  }
+
+  _accountHasInsufficientFunds = (account, minBalance) => this._getBalance(account) < minBalance;
+  _creditAccount = (account, amount) => (this.balances[account - 1] += amount);
+  _debitAccount = (account, amount) => (this.balances[account - 1] -= amount);
+  _getBalance = (account) => this.balances[account - 1];
+  _isInvalidAccount = (account) => account <= 0 || account > this.balances.length;
+
+  transfer = (fromAccount, toAccount, amount) => {
+    if (this._isInvalidAccount(fromAccount)) return false;
+    if (this._isInvalidAccount(toAccount)) return false;
+    if (this._accountHasInsufficientFunds(fromAccount, amount)) return false;
+    this._debitAccount(fromAccount, amount);
+    this._creditAccount(toAccount, amount);
+    return true;
+  };
+
+  deposit = (account, amount) => {
+    if (this._isInvalidAccount(account)) return false;
+    this._creditAccount(account, amount);
+    return true;
+  };
+
+  withdraw = (account, amount) => {
+    if (this._isInvalidAccount(account)) return false;
+    if (this._accountHasInsufficientFunds(account, amount)) return false;
+    this._debitAccount(account, amount);
+    return true;
+  };
+}

README.md

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