Longest Common Prefix in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return an empty string if the input list is empty.

DSA Python

def longest_common_prefix(strs):
    if not strs:
        return [1]

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

A''

BNone

C0

Dstrs

Attempts:

3 left

💡 Hint

Common Mistakes

Returning None instead of an empty string.

Returning 0 or the list itself.

If the list is empty, the longest common prefix is an empty string ''.

2fill in blank

medium

Complete the code to initialize the prefix as the first string in the list.

DSA Python

def longest_common_prefix(strs):
    if not strs:
        return ''
    prefix = [1]

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

A''

Bstrs[1]

Cstrs[0]

Dstrs[-1]

Attempts:

3 left

💡 Hint

Common Mistakes

Using strs[1] which may not exist or is not the first string.

Starting with an empty string which won't help find the prefix.

The prefix starts as the first string, then we compare it with others.

3fill in blank

hard

Fix the error in the loop that compares prefix with each string.

DSA Python

def longest_common_prefix(strs):
    if not strs:
        return ''
    prefix = strs[0]
    for s in strs[[1]:]:
        while not s.startswith(prefix):
            prefix = prefix[:-1]
            if not prefix:
                return ''
    return prefix

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

A0

B1

C-1

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Starting loop from 0 causes redundant comparison.

Using negative or out-of-range indices.

We start comparing from the second string, index 1, because prefix is strs[0].

4fill in blank

hard

Fill both blanks to correctly reduce the prefix until it matches the start of the string.

DSA Python

def longest_common_prefix(strs):
    if not strs:
        return ''
    prefix = strs[0]
    for s in strs[1:]:
        while not s.startswith(prefix):
            prefix = prefix[1]1
            if not prefix:
                return [2]
    return prefix

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

A[:-

B''

C[-

D[::

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect slicing syntax like prefix[+1].

Returning None instead of empty string.

prefix[:-1] removes the last character; return '' if prefix is empty.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps each word to its length if length is greater than 3.

DSA Python

words = ['apple', 'bat', 'car', 'door']
lengths = { [1] : [2] for [3] in words if len([3]) > 3 }

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

Aword

Blen(word)

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Using len(word) as key instead of value.

The comprehension uses word as key and len(word) as value, iterating over words with variable word.