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2043. Simple Bank System

Medium
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  • The amount of money withdrawn or transferred from is less than or equal to the balance of the account.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,soitisvalidtowithdraw20, so it is valid to withdraw 10.
                                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ // Account 3 has 20−20 - 10 = 10.bank.transfer(5,1,20);//returntrue,account5hasabalanceof10. bank.transfer(5, 1, 20); // return true, account 5 has a balance of 30, so it is valid to transfer 20.//Account5has20. // Account 5 has 30 - 20=20 = 10, and account 1 has 10+10 + 20 = 30.bank.deposit(5,20);//returntrue,itisvalidtodeposit30. bank.deposit(5, 20); // return true, it is valid to deposit 20 to account 5.
// Account 5 has 10+10 + 20 = 30.bank.transfer(3,4,15);//returnfalse,thecurrentbalanceofaccount3is30. 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 ≤\leq n, account, account1, account2 ≤\leq 10510^5
  • 0 ≤\leq balance[i], money ≤\leq 101210^12
  • At most 10410^4 calls will be made to each function transfer, deposit, withdraw.

解題思路​

照著題目描述並轉換成程式碼
首先初始化 Bank 物件，包含傳入的 balance 以及 n 代表 balance 的 length

var Bank = function (balance) {
  this.balance = balance;
  this.n = balance.length;
};

再分別實作轉帳、存款、提款的功能
先是轉帳

Bank.prototype.transfer = function (account1, account2, money) {
  if (account1 > this.n || account2 > this.n) return false; // 如果任一帳戶編號 > n ，代表該帳戶不存在，回傳 false
  if (money > this.balance[account1 - 1]) return false; // 如果帳戶餘額不夠也是 false

  this.balance[account1 - 1] -= money; // 從帳戶 1 轉出 money
  this.balance[account2 - 1] += money; // 把 money 轉入帳戶 2

  return true;
};

再來存款

Bank.prototype.deposit = function (account, money) {
  if (account > this.n) return false; // 如果帳戶編號 > n ，代表該帳戶不存在，回傳 false

  this.balance[account - 1] += money; // 把 money 存入該帳戶

  return true;
};

最後提款

Bank.prototype.withdraw = function (account, money) {
  if (account > this.n) return false; // 如果帳戶編號 > n ，代表該帳戶不存在，回傳 false
  if (money > this.balance[account - 1]) return false; // 如果帳戶餘額不夠也是 false

  this.balance[account - 1] -= money; // 從帳戶中轉出 money

  return true;
};

心得​

酷酷物件導向
一開始使用 !this.balance[account - 1]，來判斷帳戶是否存在
但這樣子要是帳戶餘額是 0，!0 會變成 true，導致錯誤判斷為帳戶不存在
後來改成使用 if (account > this.n) 解決此問題。

而因為物件導向很適合用來練習 TypeScript
所以也另外寫了 TS 版本的解答。
跟 JS 的邏輯是一樣的，只是變為使用 class 來實作，以及在初始化時候包含 balance 和 n 的型別來避免 IDE 報錯

class Bank {
  public balance: number[];
  public n: number;

  constructor(balance: number[]) {
    this.balance = balance;
    this.n = balance.length;
  }
}