Two Sum Problem Classic Hash Solution in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the dictionary for storing seen numbers.

DSA Python

seen = [1]

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

A[]

B{}

C()

Dset()

Attempts:

3 left

💡 Hint

Common Mistakes

Using a list or set instead of a dictionary.

Using parentheses which create a tuple, not a dictionary.

We use an empty dictionary {} to store numbers and their indices for quick lookup.

2fill in blank

medium

Complete the code to iterate over the list with index and value.

DSA Python

for [1], num in enumerate(nums):

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Ai

Bvalue

Cindex

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using the value variable name instead of index.

Using a variable name that is not descriptive or inconsistent.

The variable i is commonly used as the index in loops.

3fill in blank

hard

Fix the error in checking if the complement exists in the dictionary.

DSA Python

if [1] in seen:

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Anum

Bi

Ctarget - num

Dseen[num]

Attempts:

3 left

💡 Hint

Common Mistakes

Checking if the current number num is in seen instead of the complement.

Using the index i instead of the complement.

We check if the complement target - num is already in the dictionary seen.

4fill in blank

hard

Fill both blanks to return the indices of the two numbers that add up to target.

DSA Python

return [seen[[1]], [2]]

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Atarget - num

Bi

Cnum

Dseen[num]

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the current number instead of its index.

Swapping the order of indices incorrectly.

Return the index of the complement from seen and the current index i.

5fill in blank

hard

Fill all three blanks to add the current number and its index to the dictionary.

DSA Python

seen[[1]] = [2]

# After loop ends
return [3]

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Anum

Bi

C[]

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Using the index as key instead of the number.

Returning an empty list instead of None.

Add the current number as key and index as value to seen. Return None if no pair found.