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Java-based LeetCode algorithm problem solutions, regularly updated
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package g2001_2100.s2043_simple_bank_system;

// #Medium #Array #Hash_Table #Design #Simulation
// #2022_05_27_Time_128_ms_(72.30%)_Space_81_MB_(76.62%)

/**
 * 2043 - Simple Bank System\.
 *
 * Medium
 *
 * 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 * *   The amount of money withdrawn or transferred from is **less than or equal** to the balance of the account.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`.
**/
public class Bank {
    private final long[] accounts;

    public Bank(long[] balance) {
        accounts = balance;
    }

    private boolean validate(int account, long money, boolean withdraw) {
        return account < accounts.length && (!withdraw || accounts[account] >= money);
    }

    public boolean transfer(int account1, int account2, long money) {
        if (validate(account1 - 1, money, true) && validate(account2 - 1, 0, false)) {
            accounts[account1 - 1] -= money;
            accounts[account2 - 1] += money;
            return true;
        }
        return false;
    }

    public boolean deposit(int account, long money) {
        if (validate(account - 1, money, false)) {
            accounts[account - 1] += money;
            return true;
        }
        return false;
    }

    public boolean withdraw(int account, long money) {
        if (validate(account - 1, money, true)) {
            accounts[account - 1] -= money;
            return true;
        }
        return false;
    }
}

/*
 * Your Bank object will be instantiated and called as such:
 * Bank obj = new Bank(balance);
 * boolean param_1 = obj.transfer(account1,account2,money);
 * boolean param_2 = obj.deposit(account,money);
 * boolean param_3 = obj.withdraw(account,money);
 */