problemmediumalgorithmsleetcode-2043leetcode 2043leetcode2043

Simple Bank System

MediumUpdated: Aug 2, 2025
Practice on:
LeetCode

Problem

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  • The amount of money withdrawn or transferred from is less than or equal to the balance of the account.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

Examples

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 <= 10^5
  • 0 <= balance[i], money <= 1012
  • At most 104 calls will be made to each function transfer, deposit, withdraw.

Solution

Method 1 – Array Simulation

Intuition

Use an array to store balances. For each operation, check account validity and balance, then update accordingly.

Approach

  1. Store balances in an array (0-indexed, but accounts are 1-indexed).
  2. For each operation, check if account(s) are valid (1 <= account <= n).
  3. For withdraw/transfer, check if balance is sufficient.
  4. Update balances as needed and return True/False.

Code

C++
#include <vector>
using namespace std;
class Bank {
    vector<long long> bal;
    int n;
public:
    Bank(vector<long long>& balance) : bal(balance), n(balance.size()) {}
    bool valid(int acc) { return acc >= 1 && acc <= n; }
    bool transfer(int acc1, int acc2, long long money) {
        if (!valid(acc1) || !valid(acc2) || bal[acc1-1] < money) return false;
        bal[acc1-1] -= money; bal[acc2-1] += money; return true;
    }
    bool deposit(int acc, long long money) {
        if (!valid(acc)) return false;
        bal[acc-1] += money; return true;
    }
    bool withdraw(int acc, long long money) {
        if (!valid(acc) || bal[acc-1] < money) return false;
        bal[acc-1] -= money; return true;
    }
};
Java
class Bank {
    private long[] bal;
    private int n;
    public Bank(long[] balance) {
        bal = balance;
        n = balance.length;
    }
    private boolean valid(int acc) { return acc >= 1 && acc <= n; }
    public boolean transfer(int acc1, int acc2, long money) {
        if (!valid(acc1) || !valid(acc2) || bal[acc1-1] < money) return false;
        bal[acc1-1] -= money; bal[acc2-1] += money; return true;
    }
    public boolean deposit(int acc, long money) {
        if (!valid(acc)) return false;
        bal[acc-1] += money; return true;
    }
    public boolean withdraw(int acc, long money) {
        if (!valid(acc) || bal[acc-1] < money) return false;
        bal[acc-1] -= money; return true;
    }
}
Python
class Bank:
    def __init__(self, balance):
        self.bal = balance
        self.n = len(balance)
    def valid(self, acc):
        return 1 <= acc <= self.n
    def transfer(self, acc1, acc2, money):
        if not self.valid(acc1) or not self.valid(acc2) or self.bal[acc1-1] < money:
            return False
        self.bal[acc1-1] -= money
        self.bal[acc2-1] += money
        return True
    def deposit(self, acc, money):
        if not self.valid(acc):
            return False
        self.bal[acc-1] += money
        return True
    def withdraw(self, acc, money):
        if not self.valid(acc) or self.bal[acc-1] < money:
            return False
        self.bal[acc-1] -= money
        return True

Complexity

  • ⏰ Time complexity: O(1) per operation.
  • 🧺 Space complexity: O(n) for the balances array.

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