2043. Simple Bank System

2043. Simple Bank System

Difficulty: Medium

Topics: Array, Hash Table, Design, Simulation, Weekly Contest 263

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• The amount of money withdrawn or transferred from is less than or equal to the balance of the account.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.

Hint:

1. How do you determine if a transaction will fail?
2. Simply apply the operations if the transaction is valid.

Solution:

We need to design a banking system that handles three operations: transfer, deposit, and withdraw, with proper validation.

Approach:

• Store account balances in an array with 1-based indexing (account 1 is at index 0)
• For each operation, validate account numbers and sufficient funds
• Use basic arithmetic operations to update balances

Let's implement this solution in PHP: 2043. Simple Bank System

<?php
class Bank {
    private array $accounts;
    private int $totalAccounts;

    /**
     * @param Integer[] $balance
     */
    function __construct($balance) {
        $this->accounts = $balance;
        $this->totalAccounts = count($balance);
    }

    /**
     * @param Integer $account1
     * @param Integer $account2
     * @param Integer $money
     * @return Boolean
     */
    function transfer($account1, $account2, $money) {
       ...
       ...
       ...
       /**
        * go to ./solution.php
        */
    }

    /**
     * @param Integer $account
     * @param Integer $money
     * @return Boolean
     */
    function deposit($account, $money) {
       ...
       ...
       ...
       /**
        * go to ./solution.php
        */
    }

    /**
     * @param Integer $account
     * @param Integer $money
     * @return Boolean
     */
    function withdraw($account, $money) {
       ...
       ...
       ...
       /**
        * go to ./solution.php
        */
    }

    /**
     * Check if account number is valid (between 1 and totalAccounts)
     *
     * @param int $account
     * @return bool
     */
    private function isValidAccount(int $account): bool {
       ...
       ...
       ...
       /**
        * go to ./solution.php
        */
    }

    /**
     * Debug: Get current balances (for testing/demo purposes).
     *
     * @return array
     */
    public function getBalances(): array {
       ...
       ...
       ...
       /**
        * go to ./solution.php
        */
    }
}

// Test cases
$bank = new Bank([10, 100, 20, 50, 30]);

echo json_encode([
    $bank->withdraw(3, 10),    // true
    $bank->transfer(5, 1, 20), // true
    $bank->deposit(5, 20),     // true
    $bank->transfer(3, 4, 15), // false
    $bank->withdraw(10, 50)    // false
]) . PHP_EOL;

// Optional: show final balances
print_r($bank->getBalances());
?>

Explanation:

1. Constructor: Initializes the bank with account balances and stores the total number of accounts.

2. Transfer:

   • Validates both source and destination accounts exist
   • Checks if source account has sufficient funds
   • Transfers money by subtracting from source and adding to destination

3. Deposit:

   • Validates the account exists
   • Adds money to the specified account

4. Withdraw:

   • Validates the account exists
   • Checks if account has sufficient funds
   • Subtracts money from the account

5. Helper method: isValidAccount() checks if an account number is within the valid range (1 to n).

Key Points:

• Uses 1-based indexing for accounts (account 1 is at index 0)
• All operations return boolean indicating success/failure
• Proper validation prevents invalid transactions
• Time complexity: O(1) for all operations
• Space complexity: O(n) where n is the number of accounts

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