Layer 2 solutions overview in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary purpose of Layer 2 solutions?

Layer 2 solutions are designed to improve blockchain networks. What is their main goal?

A To create new cryptocurrencies unrelated to the main chain

B To increase transaction speed and reduce fees by processing transactions off the main chain

C To replace the main blockchain with a new one

D To increase the size of blocks on the main chain

💡 Hint

Think about how Layer 2 helps with congestion on the main blockchain.

Layer 2 solutions work by handling transactions outside the main blockchain, which helps speed up processing and lowers fees.

❓ Predict Output

intermediate

Output of a simple state channel transaction update

Consider this pseudocode for a state channel updating balances off-chain:

channel_state = {'Alice': 5, 'Bob': 5}
channel_state['Alice'] -= 2
channel_state['Bob'] += 2
print(channel_state)

What is the output?

Blockchain / Solidity

channel_state = {'Alice': 5, 'Bob': 5}
channel_state['Alice'] -= 2
channel_state['Bob'] += 2
print(channel_state)

A {'Alice': 3, 'Bob': 7}

B {'Alice': 7, 'Bob': 3}

C {'Alice': 5, 'Bob': 5}

D TypeError: unsupported operand type(s)

💡 Hint

Subtract 2 from Alice's balance and add 2 to Bob's.

The code deducts 2 from Alice and adds 2 to Bob, updating the balances accordingly.

🔧 Debug

advanced

Identify the error in this optimistic rollup code snippet

Review this simplified pseudocode for an optimistic rollup submission:

def submit_batch(batch):
    if len(batch) == 0:
        raise ValueError('Batch cannot be empty')
    process(batch)

What error will this code produce when run?

Blockchain / Solidity

def submit_batch(batch):
    if len(batch) == 0:
        raise ValueError('Batch cannot be empty')
    process(batch)

A No error, runs successfully

B NameError because process is undefined

C SyntaxError due to missing colon after if statement

D ValueError because batch is empty

💡 Hint

Check the syntax of the if statement.

The if statement is missing a colon at the end, causing a SyntaxError.

❓ Predict Output

advanced

Result of Plasma exit challenge simulation

Given this pseudocode simulating a Plasma exit challenge:

exits = {'user1': 100}
challenge_amount = 50
exits['user1'] -= challenge_amount
print(exits['user1'])

What is printed?

Blockchain / Solidity

exits = {'user1': 100}
challenge_amount = 50
exits['user1'] -= challenge_amount
print(exits['user1'])

A KeyError

B 150

C 100

D 50

💡 Hint

Subtract challenge_amount from the user's exit amount.

The code subtracts 50 from 100, leaving 50 as the new exit amount.

🧠 Conceptual

expert

Which Layer 2 solution uses zero-knowledge proofs to validate transactions?

Among Layer 2 solutions, which one relies on zero-knowledge proofs to ensure transaction validity without revealing data?

A ZK Rollups

B Plasma

C State Channels

D Optimistic Rollups

💡 Hint

Zero-knowledge proofs are a key feature of one Layer 2 type that compresses data and proofs.

ZK Rollups use zero-knowledge proofs to validate transactions off-chain and submit succinct proofs on-chain.