2043. Simple Bank System
Approach
Store balances in array; validate account indices on each operation.
Key Techniques
Array problems involve manipulating elements stored in a contiguous block of memory. Key techniques include two-pointer traversal, prefix sums, sliding windows, and in-place partitioning. In C#, arrays are zero-indexed and fixed in size — use List<T> when you need dynamic resizing.
Hash tables provide O(1) average-case lookup, insert, and delete. They are the go-to tool for counting frequencies, detecting complements (Two Sum pattern), and caching seen values. In C#, use Dictionary<K,V> for maps and HashSet<T> for membership checks.
Design problems ask you to implement a data structure or system with specific API contracts. Common designs: LRU Cache (HashMap + doubly linked list), LFU Cache, Min Stack, Iterator, and streaming median. Focus on the time complexity required for each operation.
// Approach: Store balances in array; validate account indices on each operation.
// Time: O(1) per op Space: O(n)
public class Bank
{
// Array to store account balances
private long[] accountBalances;
// Total number of accounts in the bank
private int numberOfAccounts;
/// <summary>
/// Constructor to initialize the bank with initial account balances
/// </summary>
/// <param name="balance">Array of initial balances for each account</param>
public Bank(long[] balance)
{
this.accountBalances = balance;
this.numberOfAccounts = balance.Length;
}
/// <summary>
/// Transfer money from one account to another
/// </summary>
/// <param name="account1">Source account number (1-indexed)</param>
/// <param name="account2">Destination account number (1-indexed)</param>
/// <param name="money">Amount of money to transfer</param>
/// <returns>true if transfer is successful, false otherwise</returns>
public bool Transfer(int account1, int account2, long money)
{
// Validate both account numbers exist and source account has sufficient balance
if (account1 > numberOfAccounts || account2 > numberOfAccounts ||
accountBalances[account1 - 1] < money)
return false;
// Deduct money from source account
accountBalances[account1 - 1] -= money;
// Add money to destination account
accountBalances[account2 - 1] += money;
return true;
}
/// <summary>
/// Deposit money into an account
/// </summary>
/// <param name="account">Account number (1-indexed)</param>
/// <param name="money">Amount of money to deposit</param>
/// <returns>true if deposit is successful, false otherwise</returns>
public bool Deposit(int account, long money)
{
// Validate account number exists
if (account > numberOfAccounts)
return false;
// Add money to the account
accountBalances[account - 1] += money;
return true;
}
/// <summary>
/// Withdraw money from an account
/// </summary>
/// <param name="account">Account number (1-indexed)</param>
/// <param name="money">Amount of money to withdraw</param>
/// <returns>true if withdrawal is successful, false otherwise</returns>
public bool Withdraw(int account, long money)
{
// Validate account number exists and has sufficient balance
if (account > numberOfAccounts || accountBalances[account - 1] < money)
return false;
// Deduct money from the account
accountBalances[account - 1] -= money;
return true;
}
}
/**
* Your Bank object will be instantiated and called as such:
* Bank obj = new Bank(balance);
* bool param_1 = obj.Transfer(account1,account2,money);
* bool param_2 = obj.Deposit(account,money);
* bool param_3 = obj.Withdraw(account,money);
*/