Simplify debts algorithm in LLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the net balance for each person.

LLD

net_balance = {person: 0 for person in [1]

Drag options to blanks, or click blank then click option'

Atransactions

Bpeople

Cdebts

Dbalances

Attempts:

3 left

💡 Hint

Common Mistakes

Using debts or transactions instead of the list of people.

Initializing net_balance with an empty dictionary without keys.

We initialize net_balance for each person in the list people.

2fill in blank

medium

Complete the code to update net balances after each transaction.

LLD

net_balance[debtor] [1]= amount
net_balance[creditor] [1]= -amount

Drag options to blanks, or click blank then click option'

A-

B/

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition for debtor's balance which increases it incorrectly.

Using multiplication or division which are not relevant here.

Debtor's balance decreases by amount, creditor's balance increases by amount, so debtor subtracts amount and creditor adds amount (negative subtract equals add).

3fill in blank

hard

Fix the error in the code to find the person with maximum credit.

LLD

max_credit_person = max(net_balance, key=lambda x: net_balance[[1]])

Drag options to blanks, or click blank then click option'

Amax_credit_person

Bperson

Cnet_balance

Dx

Attempts:

3 left

💡 Hint

Common Mistakes

Using net_balance or max_credit_person inside the lambda instead of the parameter.

Using a variable not defined in the lambda parameter list.

The lambda function parameter x is used to access net_balance[x].

4fill in blank

hard

Fill both blanks to correctly update balances after settling debts.

LLD

settle_amount = min(net_balance[[1]], -net_balance[[2]])
net_balance[[1]] -= settle_amount
net_balance[[2]] += settle_amount

Drag options to blanks, or click blank then click option'

Amax_credit_person

Bmax_debit_person

Cdebtor

Dcreditor

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping creditor and debtor in the blanks.

Using unrelated variable names.

We settle debts between the person with max credit and max debit.

5fill in blank

hard

Fill all three blanks to create the final simplified debts record.

LLD

if settle_amount > 0:
    simplified_debts.append(([1], [2], [3]))

Drag options to blanks, or click blank then click option'

Amax_debit_person

Bmax_credit_person

Csettle_amount

Dnet_balance

Attempts:

3 left

💡 Hint

Common Mistakes

Reversing debtor and creditor in the tuple.

Using net_balance instead of settle_amount for the amount.

The simplified debt is from debtor to creditor with the settled amount.

Practice

1. What is the main goal of the Simplify debts algorithm in group expense management?

easy

A. To calculate individual spending only

B. To increase the number of transactions

C. To reduce multiple debts into fewer payments

D. To create more complex debt chains

Solution

1. Step 1: Understand the purpose of the algorithm

   The algorithm aims to make settling debts easier by reducing the number of payments needed.

2. Step 2: Identify the effect on transactions

   It simplifies the process by minimizing transactions, not increasing them.

3. Final Answer:

   To reduce multiple debts into fewer payments -> Option C

4. Quick Check:

   Simplify debts = fewer payments [OK]

Hint: Focus on reducing payments, not increasing them [OK]

Common Mistakes:

• Thinking it increases transactions
• Confusing with individual spending calculation
• Assuming it complicates debt chains

2. Which of the following is the correct way to represent a person's net balance in a debts simplification system?

easy

A. A zero value means the person neither owes nor is owed money

B. A negative value means the person is owed money

C. Net balance is always zero for all participants

D. A positive value means the person owes money

Solution

1. Step 1: Understand net balance meaning

   Positive net balance means the person should receive money; negative means they owe money.

2. Step 2: Interpret zero net balance

   If net balance is zero, the person neither owes nor is owed money.

3. Final Answer:

   A zero value means the person neither owes nor is owed money -> Option A

4. Quick Check:

   Zero net balance = no debt [OK]

Hint: Zero net balance means no money owed or owed to you [OK]

Common Mistakes:

• Mixing positive and negative meanings
• Assuming net balance is always zero
• Confusing who owes and who is owed

3. Given the net balances: Alice: +50, Bob: -30, Charlie: -20, what is the minimum number of transactions to settle debts using the simplify debts algorithm?

medium

A. 2 transactions

B. 3 transactions

C. 1 transaction

D. 4 transactions

Solution

1. Step 1: Analyze net balances

   Alice is owed 50, Bob owes 30, Charlie owes 20.

2. Step 2: Match debtors with creditor

   Bob pays Alice 30, Charlie pays Alice 20, totaling 2 transactions.

3. Final Answer:

   2 transactions -> Option A

4. Quick Check:

   Sum debts to creditor = 2 transactions [OK]

Hint: Match debtors to creditors directly to minimize transactions [OK]

Common Mistakes:

• Counting each debt separately without simplification
• Assuming one transaction can cover all debts
• Misallocating amounts between participants

4. In the following code snippet for simplifying debts, what is the error?

net_balances = {"A": 40, "B": -40}
for person, balance in net_balances.items():
    if balance > 0:
        print(f"{person} owes money")
    else:
        print(f"{person} is owed money")

medium

A. The loop should use net_balances.keys() instead of items()

B. The condition for owing money is reversed

C. The print statements are missing parentheses

D. The dictionary keys should be integers, not strings

Solution

1. Step 1: Check condition logic

   Positive balance means the person is owed money, not owes money.

2. Step 2: Verify print statements

   Print syntax is correct; keys as strings are valid in Python.

3. Final Answer:

   The condition for owing money is reversed -> Option B

4. Quick Check:

   Positive balance = owed money, not owes [OK]

Hint: Positive balance means you get money, not owe it [OK]

Common Mistakes:

• Confusing who owes and who is owed
• Incorrect loop usage assumptions
• Syntax errors that don't exist here

5. You have a group with net balances: Dave: +70, Emma: -50, Frank: -20. How would you apply the simplify debts algorithm to minimize transactions and what are the transactions?

hard

A. Emma pays Frank 20, Frank pays Dave 50 (2 transactions)

B. Dave pays Emma 50, Dave pays Frank 20 (2 transactions)

C. Emma pays Dave 70, Frank pays Emma 0 (2 transactions)

D. Emma pays Dave 50, Frank pays Dave 20 (2 transactions)

Solution

1. Step 1: Identify creditors and debtors

   Dave is owed 70, Emma owes 50, Frank owes 20.

2. Step 2: Match debtors to creditor to minimize transactions

   Emma pays Dave 50, Frank pays Dave 20, totaling 2 transactions.

3. Final Answer:

   Emma pays Dave 50, Frank pays Dave 20 (2 transactions) -> Option D

4. Quick Check:

   Debtors pay creditor directly = 2 transactions [OK]

Hint: Debtors pay creditor amounts equal to their debts [OK]

Common Mistakes:

• Reversing payer and receiver roles
• Assigning incorrect amounts
• Adding unnecessary transactions