LeetCode 2043. Simple Bank System

原题链接在这里：https://leetcode.com/problems/simple-bank-system/description/

题目：

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• The amount of money withdrawn or transferred from is less than or equal to the balance of the account.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

题解：

Check account index is there before deposit.

Check account index is there and if enough balance before withdraw.

For transfer, check account2 exists and if withdraw from account1 success, then return deposit to account2.

Note: need to check account2 exists first, otherwise, the withdraw happens, but deposit is not there, then the money is lost.

Time Complexity: transfer, O(1). deposit, O(1). withdraw, O(1).

Space: O(1).

AC Java:

class Bank {
    long[] balance;

    public Bank(long[] balance) {
        this.balance = balance;    
    }
    
    public boolean transfer(int account1, int account2, long money) {
        if(account2 <= balance.length && withdraw(account1, money)){
            return deposit(account2, money);
        }

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

        return false;
    }
    
    public boolean withdraw(int account, long money) {
        if(account <= balance.length && balance[account - 1] >= money){
            balance[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);
 */