# 2043. Simple Bank System

## Description

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• The amount of money withdrawn or transferred from is less than or equal to the balance of the account.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

## Solutions

Solution 1: Simulation

According to the problem description, we can use an array balance to simulate the balance of bank accounts. The array index starts from 0, and the value of the array represents the balance of the account.

• During initialization, we assign the balance array to the member variable this.balance, and assign the length of balance to the member variable this.n.
• In the transfer function, if account1 or account2 is greater than n or balance[account1 - 1] is less than money, return false. Otherwise, subtract money from balance[account1 - 1], add money to balance[account2 - 1], and return true.
• In the deposit function, if account is greater than n, return false. Otherwise, add money to balance[account - 1], and return true.
• In the withdraw function, if account is greater than n or balance[account - 1] is less than money, return false. Otherwise, subtract money from balance[account - 1], and return true.

The time complexity of the above operations is $O(1)$, and the space complexity is $O(n)$. Here, $n$ is the length of balance.

• class Bank {
private long[] balance;
private int n;

public Bank(long[] balance) {
this.balance = balance;
this.n = balance.length;
}

public boolean transfer(int account1, int account2, long money) {
if (account1 > n || account2 > n || balance[account1 - 1] < money) {
return false;
}
balance[account1 - 1] -= money;
balance[account2 - 1] += money;
return true;
}

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

public boolean withdraw(int account, long money) {
if (account > n || balance[account - 1] < money) {
return false;
}
balance[account - 1] -= money;
return true;
}
}

/**
* 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);
*/

• class Bank {
public:
vector<long long> balance;
int n;

Bank(vector<long long>& balance) {
this->balance = balance;
n = balance.size();
}

bool transfer(int account1, int account2, long long money) {
if (account1 > n || account2 > n || balance[account1 - 1] < money) return false;
balance[account1 - 1] -= money;
balance[account2 - 1] += money;
return true;
}

bool deposit(int account, long long money) {
if (account > n) return false;
balance[account - 1] += money;
return true;
}

bool withdraw(int account, long long money) {
if (account > n || balance[account - 1] < money) return false;
balance[account - 1] -= money;
return true;
}
};

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

• class Bank:
def __init__(self, balance: List[int]):
self.balance = balance
self.n = len(balance)

def transfer(self, account1: int, account2: int, money: int) -> bool:
if account1 > self.n or account2 > self.n or self.balance[account1 - 1] < money:
return False
self.balance[account1 - 1] -= money
self.balance[account2 - 1] += money
return True

def deposit(self, account: int, money: int) -> bool:
if account > self.n:
return False
self.balance[account - 1] += money
return True

def withdraw(self, account: int, money: int) -> bool:
if account > self.n or self.balance[account - 1] < money:
return False
self.balance[account - 1] -= money
return True

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


• type Bank struct {
balance []int64
n       int
}

func Constructor(balance []int64) Bank {
return Bank{balance, len(balance)}
}

func (this *Bank) Transfer(account1 int, account2 int, money int64) bool {
if account1 > this.n || account2 > this.n || this.balance[account1-1] < money {
return false
}
this.balance[account1-1] -= money
this.balance[account2-1] += money
return true
}

func (this *Bank) Deposit(account int, money int64) bool {
if account > this.n {
return false
}
this.balance[account-1] += money
return true
}

func (this *Bank) Withdraw(account int, money int64) bool {
if account > this.n || this.balance[account-1] < money {
return false
}
this.balance[account-1] -= money
return true
}

/**
* Your Bank object will be instantiated and called as such:
* obj := Constructor(balance);
* param_1 := obj.Transfer(account1,account2,money);
* param_2 := obj.Deposit(account,money);
* param_3 := obj.Withdraw(account,money);
*/

• class Bank {
balance: number[];
constructor(balance: number[]) {
this.balance = balance;
}

transfer(account1: number, account2: number, money: number): boolean {
if (
account1 > this.balance.length ||
account2 > this.balance.length ||
money > this.balance[account1 - 1]
)
return false;
this.balance[account1 - 1] -= money;
this.balance[account2 - 1] += money;
return true;
}

deposit(account: number, money: number): boolean {
if (account > this.balance.length) return false;
this.balance[account - 1] += money;
return true;
}

withdraw(account: number, money: number): boolean {
if (account > this.balance.length || money > this.balance[account - 1]) {
return false;
}
this.balance[account - 1] -= money;
return true;
}
}

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


• struct Bank {
balance: Vec<i64>,
}

/**
* &self means the method takes an immutable reference.
* If you need a mutable reference, change it to &mut self instead.
*/
impl Bank {
fn new(balance: Vec<i64>) -> Self {
Bank { balance }
}

fn transfer(&mut self, account1: i32, account2: i32, money: i64) -> bool {
let (account1, account2, n) = (account1 as usize, account2 as usize, self.balance.len());
if n < account1 || n < account2 {
return false;
}
if self.balance[account1 - 1] < money {
return false;
}
self.balance[account1 - 1] -= money;
self.balance[account2 - 1] += money;
true
}

fn deposit(&mut self, account: i32, money: i64) -> bool {
let (account, n) = (account as usize, self.balance.len());
if n < account {
return false;
}
self.balance[account - 1] += money;
true
}

fn withdraw(&mut self, account: i32, money: i64) -> bool {
let (account, n) = (account as usize, self.balance.len());
if n < account {
return false;
}
if self.balance[account - 1] < money {
return false;
}
self.balance[account - 1] -= money;
true
}
}/**
* Your Bank object will be instantiated and called as such:
* let obj = Bank::new(balance);
* let ret_1: bool = obj.transfer(account1, account2, money);
* let ret_2: bool = obj.deposit(account, money);
* let ret_3: bool = obj.withdraw(account, money);
*/