Simple Bank System
<p>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 <code>n</code> accounts numbered from <code>1</code> to <code>n</code>. The initial balance of each account is stored in a <strong>0-indexed</strong> integer array <code>balance</code>, with the <code>(i + 1)<sup>th</sup></code> account having an initial balance of <code>balance[i]</code>.</p>

<p>Execute all the <strong>valid</strong> transactions. A transaction is <strong>valid</strong> if:</p>

<ul>
	<li>The given account number(s) are between <code>1</code> and <code>n</code>, and</li>
	<li>The amount of money withdrawn or transferred from is <strong>less than or equal</strong> to the balance of the account.</li>
</ul>

<p>Implement the <code>Bank</code> class:</p>

<ul>
	<li><code>Bank(long[] balance)</code> Initializes the object with the <strong>0-indexed</strong> integer array <code>balance</code>.</li>
	<li><code>boolean transfer(int account1, int account2, long money)</code> Transfers <code>money</code> dollars from the account numbered <code>account1</code> to the account numbered <code>account2</code>. Return <code>true</code> if the transaction was successful, <code>false</code> otherwise.</li>
	<li><code>boolean deposit(int account, long money)</code> Deposit <code>money</code> dollars into the account numbered <code>account</code>. Return <code>true</code> if the transaction was successful, <code>false</code> otherwise.</li>
	<li><code>boolean withdraw(int account, long money)</code> Withdraw <code>money</code> dollars from the account numbered <code>account</code>. Return <code>true</code> if the transaction was successful, <code>false</code> otherwise.</li>
</ul>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input</strong>
[&quot;Bank&quot;, &quot;withdraw&quot;, &quot;transfer&quot;, &quot;deposit&quot;, &quot;transfer&quot;, &quot;withdraw&quot;]
[[[10, 100, 20, 50, 30]], [3, 10], [5, 1, 20], [5, 20], [3, 4, 15], [10, 50]]
<strong>Output</strong>
[null, true, true, true, false, false]

<strong>Explanation</strong>
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.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>n == balance.length</code></li>
	<li><code>1 &lt;= n, account, account1, account2 &lt;= 10<sup>5</sup></code></li>
	<li><code>0 &lt;= balance[i], money &lt;= 10<sup>12</sup></code></li>
	<li>At most <code>10<sup>4</sup></code> calls will be made to <strong>each</strong> function <code>transfer</code>, <code>deposit</code>, <code>withdraw</code>.</li>
</ul>
Design; Array; Hash Table; Simulation
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);
 */