First Non Repeating Character Using Hash in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a dictionary to count characters.

DSA Python

count = [1]()

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Adict

Blist

Cset

Dtuple

Attempts:

3 left

💡 Hint

Common Mistakes

Using list or set instead of dictionary for counting.

Trying to use tuple which is immutable.

We use dict() to create a dictionary for counting characters.

2fill in blank

medium

Complete the code to increment the count of character c in the dictionary.

DSA Python

count[c] = count.get(c, 0) [1] 1

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A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using minus or multiplication instead of addition.

Forgetting to handle the default count with get.

We add 1 to the current count to increment the character count.

3fill in blank

hard

Fix the error in the loop to find the first non-repeating character.

DSA Python

for c in s:
    if count[c] == [1]:
        return c

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A0

B-1

C2

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for count 0 or 2 instead of 1.

Using negative numbers which don't make sense here.

The first non-repeating character has a count of exactly 1.

4fill in blank

hard

Fill both blanks to complete the function that returns the first non-repeating character or '_' if none.

DSA Python

def first_non_repeating(s):
    count = dict()
    for c in s:
        count[c] = count.get(c, 0) [1] 1
    for c in s:
        if count[c] == [2]:
            return c
    return '_'

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

A+

B-

C1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong operators for increment.

Checking for count 0 instead of 1.

We increment counts by 1 and check if count equals 1 for non-repeating characters.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that counts characters appearing more than once.

DSA Python

count = [1]( (c, s.count(c)) for c in s if s.count(c) [2] [3] )

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

Adict

B>

C1

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using list or set instead of dict.

Using less than instead of greater than.

Checking for count equal to 1 instead of greater than 1.

We use dict to create the dictionary, check if count is greater than 1 to find repeating characters.