Problem Statement in English

You have been tasked with implementing a simple bank system that supports three operations: transfer, deposit, and withdraw.

The bank system should maintain account balances and ensure that all operations are valid.

Bank accounts are numbered from 1 to n, where n is the total number of accounts. Each account has an initial balance.

Approach

We can use a hashmap to store the account balances.

Each operation (transfer, deposit, withdraw) can be performed in constant time by checking and updating the balances in the hashmap.

Solution in Python


class Bank:

    def __init__(self, balance: List[int]):
        self.hm = {}
        self.n = len(balance)

        for i in range(len(balance)):
            self.hm[i + 1] = balance[i]

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

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

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

Complexity

  • Time: $O(1)$ for all operations except the initialization, which is $O(n)$

  • Space: $O(n)$
    Since we use a hashmap

And we are done.