What is the time complexity of Simple Bank System?

The optimal solution has a time complexity of O(1).

What data structures are used to solve Simple Bank System?

This problem uses Array, Hash Table, Design, Simulation. Understanding these concepts is essential for solving this Medium problem efficiently.

What are the key insights for solving Simple Bank System?

Insight 1: Direct array access is efficient for accessing account balances, given account numbers are sequential (1 to n). Insight 2: Input validation is crucial to ensure accounts exist and balances are sufficient before processing transactions.

Which companies ask LeetCode 2043. Simple Bank System in interviews?

This problem is frequently asked at Airbnb, Capital One, Circle, Coinbase, Dropbox and 1 more companies.

JavaScript is required for the full interactive experience. However, all content is accessible without JavaScript.

Simple Bank System - LeetCode 2043 Solution

Simple Bank System - Complete Solution Guide

Simple Bank System is LeetCode problem 2043, a Medium level challenge. This complete guide provides step-by-step explanations, multiple solution approaches, and optimized code in python3, java, cpp, c.

Problem Statement

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 A transaction is valid if: The given account number(s) are between 1 and n , and The amount of money withdrawn or t

Detailed Explanation

The problem simulates a simplified banking system. You're given an initial balance for each account, and you need to implement methods to transfer, deposit, and withdraw money. The key is to ensure transactions are valid: account numbers must be within the valid range (1 to n, where n is the number of accounts), and withdrawals/transfers must not exceed the account's balance. The Bank class should be initialized with an array representing initial balances. The methods `transfer`, `deposit`, and `withdraw` should return `true` if the transaction is successful and `false` otherwise.

Solution Approach

The solution uses a simple array to store account balances. Each operation (transfer, deposit, withdraw) involves checking for valid account numbers and sufficient balance. Array indices are adjusted to account for 0-based indexing while account numbers are 1-based.

Step-by-Step Algorithm

Step 1: Initialize the Bank object with the initial balances, storing them in an array.
Step 2: In the transfer method, first check if account1 and account2 are valid account numbers (between 1 and n, inclusive).
Step 3: If account numbers are valid, check if account1 has sufficient balance to transfer 'money'.
Step 4: If both conditions are met, subtract 'money' from account1's balance and add 'money' to account2's balance. Return true.
Step 5: In the deposit method, check if the account number is valid (between 1 and n, inclusive).
Step 6: If the account number is valid, add 'money' to the account's balance. Return true.
Step 7: In the withdraw method, check if the account number is valid (between 1 and n, inclusive).
Step 8: If the account number is valid, check if the account has sufficient balance to withdraw 'money'.
Step 9: If both conditions are met, subtract 'money' from the account's balance. Return true.
Step 10: If any check fails (invalid account or insufficient balance), return false.

Key Insights

Insight 1: Direct array access is efficient for accessing account balances, given account numbers are sequential (1 to n).
Insight 2: Input validation is crucial to ensure accounts exist and balances are sufficient before processing transactions.
Insight 3: Using long data types is essential to handle large balances and prevent integer overflow issues during calculations.

Complexity Analysis

Time Complexity: O(1)

Space Complexity: O(n)

Topics

This problem involves: Array, Hash Table, Design, Simulation.

Companies

Asked at: Airbnb, Capital One, Circle, Coinbase, Dropbox, PhonePe.

Simple Bank System | LeetCode 2043

Medium

Array Hash Table Design Simulation

Time: O(1)Space: O(n)

Solution Code

Available in:

class Bank {

    private long[] balance;
    private int n;

    public Bank(long[] balance) {
        this.balance = balance;
        this.n = balance.length;
    }
    
    public boolean transfer(int account1, int account2, long money) {
        if (!(1 <= account1 && account1 <= this.n && 1 <= account2 && account2 <= this.n)) {
            return false;
        }
        
        if (this.balance[account1 - 1] < money) {
            return false;
        }
            
        this.balance[account1 - 1] -= money;
        this.balance[account2 - 1] += money;
        return true;
    }
    
    public boolean deposit(int account, long money) {
        if (!(1 <= account && account <= this.n)) {
            return false;
        }
            
        this.balance[account - 1] += money;
        return true;
    }
    
    public boolean withdraw(int account, long money) {
        if (!(1 <= account && account <= this.n)) {
            return false;
        }
        
        if (this.balance[account - 1] < money) {
            return false;
        }
        
        this.balance[account - 1] -= money;
        return true;
    }
}

/**
 * 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);
 */

View Full Solution on GitHubGitHub Solution View on LeetCodeLeetCode

Problem Info

Description

Problem 2043: Simple Bank System - Detailed explanation and solution approaches.

Topics

Array Hash Table Design Simulation

Companies

AirbnbCapital OneCircleCoinbaseDropboxPhonePe

Stats

Difficulty:Medium

Languages:4

Companies:6

Problem #:2043

Problem Explanation

💡

Think Before You Code

🤔 Ask Yourself

→What is the input? What output do I need?
→Can I solve a smaller version of this problem first?
→What patterns have I seen in similar problems?

✏️ Try This First

Before looking at the solution, try to solve it on paper with a simple example!

🚀 Try on LeetCode

Solution Approach

📋

Step-by-Step Solution

10 steps

1
Step 1: Initialize the Bank object with the initial balances, storing them in an array.
2
Step 2: In the transfer method, first check if account1 and account2 are valid account numbers (between 1 and n, inclusive).
3
Step 3: If account numbers are valid, check if account1 has sufficient balance to transfer 'money'.
4
Step 4: If both conditions are met, subtract 'money' from account1's balance and add 'money' to account2's balance. Return true.
5
Step 5: In the deposit method, check if the account number is valid (between 1 and n, inclusive).
6
Step 6: If the account number is valid, add 'money' to the account's balance. Return true.
7
Step 7: In the withdraw method, check if the account number is valid (between 1 and n, inclusive).
8
Step 8: If the account number is valid, check if the account has sufficient balance to withdraw 'money'.
9
Step 9: If both conditions are met, subtract 'money' from the account's balance. Return true.
10
Step 10: If any check fails (invalid account or insufficient balance), return false.

💡

Pro Tip for Students

Try tracing through each step with a small example on paper before coding. Understanding "why" each step happens is more important than memorizing the code!

⚡

Complexity Analysis

⏱️

Time Complexity

O(1)

⚡ Constant time - Super fast! Same speed regardless of input size.

💾

Space Complexity

O(n)

📦 Linear space - Memory grows with input size.

📝

Why?

Each of the bank operations involves a constant number of operations: checking account validity, comparing balances, and updating balances. Array access is O(1). The space complexity is determined by the need to store the initial balance of each account, which requires O(n) space.

📖New to Big O? Click to learn more

Big O Notation - Quick Guide

O(1)Best - Instant

O(log n)Excellent - Binary Search

O(n)Good - One loop

O(n log n)OK - Sorting

O(n²)Slow - Nested loops

O(2ⁿ)Very Slow - Recursion

Alternative Approaches

Hash Table

Using a hash table (dictionary) to store account balances. Account numbers would be keys, and balances would be values.

Time: O(1) on average for all operations.Space: O(n) where n is the number of accounts.

Trade-offs: This approach is useful if account numbers are not sequential and may be sparse. For sequential numbering, the array based solution is better due to lower overhead. With a hash table, lookups might have rare O(n) time complexity in worst-case scenarios with hash collisions. Array lookups have constant time.

✨

Key Insights

1Insight 1: Direct array access is efficient for accessing account balances, given account numbers are sequential (1 to n).
2Insight 2: Input validation is crucial to ensure accounts exist and balances are sufficient before processing transactions.
3Insight 3: Using long data types is essential to handle large balances and prevent integer overflow issues during calculations.

📚

Key Terms Explained

For Students

Array

A collection of items stored at contiguous memory locations. Like a row of boxes.

Hash Table

A data structure that maps keys to values for quick lookup. Like a dictionary!

Edge Cases

Edge case 1: Account number is out of range (less than 1 or greater than n). Solution returns `false` without attempting any operation.
Edge case 2: Attempting to withdraw or transfer more money than the account balance. Solution returns `false` without modifying the balance.
Edge case 3: Large balance or money values to prevent Integer overflow. The code uses `long` data types in Java and C++, `long long` in C, and `int` in Python, which handles big integers by default.

⚠️

Common Mistakes to Avoid

✗Common mistake 1: Forgetting to check for valid account numbers before performing any operations. This can lead to array out-of-bounds errors.

✗Common mistake 2: Using integer data types instead of long data types for balances, leading to potential overflow issues when dealing with large amounts of money.

✗Common mistake 3: Not adjusting for the zero-based indexing of the array when accessing account balances (account numbers are 1-based).

✅

Learning Tip

Every mistake is a learning opportunity! When you make an error, understand why it happened before moving on.

🌍

Where is This Used in Real Life?

💼Real-world scenario 1: Banking systems for managing account balances and processing transactions.

🏦Real-world scenario 2: E-commerce platforms for handling payments and refunds.

🎮Real-world scenario 3: Financial software for simulating and analyzing financial transactions.

💡Understanding real-world applications helps you see the "why" behind algorithms. It's not just about passing interviews—these concepts power the apps and websites you use every day!

Author's Notes

💡 Key Insight

When dealing with arrays, always consider if sorting would simplify the problem. Many array problems have O(n) solutions using hash maps or two-pointer technique.

🎯 Interview Tip

Medium problems are the bread and butter of technical interviews. Practice explaining your approach before coding.

⚠️ Watch Out

Off-by-one errors are the most common mistake. Double-check your loop bounds and array indices.

Written by Saswata Mondal

Software Engineer • Algorithms Enthusiast • Interview Coach

👨‍💻

About the Author

👨‍💻

Saswata MondalAuthor400+ LC Problems

B.Tech CSE, IEM Kolkata | LeetCode Rating: 1672 (Top 15%)

Certified: IBM Java Developer, NPTEL Programming in Java

Last updated: August 3, 2024LeetCode Profile GitHub

This solution has been crafted based on my experience solving 400+ LeetCode problems. Each explanation is designed to help you understand the underlying concepts, not just memorize the code.

Community Tips & Insights

Try solving this without using extra space first. It's a great exercise for understanding the underlying pattern.

@CodeNinjaJul 13

In a real interview, always clarify constraints first. Ask about input size and value ranges.

@TechLeadJul 6

Don't forget to handle the edge case when the input is empty. Many candidates miss this in interviews.

@DevExpert92Jun 29

❓

Frequently Asked Questions

When should I use in-place modification vs creating a new array?

Use in-place modification when space complexity matters (O(1) space requirement) and the original array can be modified. Create a new array when you need to preserve the original data or when the problem involves significant restructuring that would complicate in-place logic.

How do I choose between a hash map and a hash set?

Use a hash set when you only need to track presence/absence of elements (like detecting duplicates). Use a hash map when you need to associate values with keys (like counting frequencies or storing indices). Hash sets use less memory since they only store keys.

How much time should I spend on a medium problem in interviews?

In a 45-minute interview, aim for: 5-10 minutes understanding and clarifying, 5-10 minutes discussing approach, 20-25 minutes coding, and 5-10 minutes testing. If stuck after 15 minutes of thinking, verbalize your thought process and ask for hints.

What is the importance of time and space complexity analysis?

Complexity analysis is crucial because: 1) Interviewers always ask about it, 2) It helps you choose between approaches, 3) It demonstrates CS fundamentals. Always state both time and space complexity, and be prepared to explain how you derived them.

What is the optimal approach for "Simple Bank System"?

For this medium-level Array problem, the key is to identify the core pattern. Analyze the input constraints to determine acceptable time complexity. Consider whether hash table techniques can optimize the solution. Always handle edge cases and validate your approach with examples before coding.

🤖 Need help with this problem?