String Traversal and Character Access in DSA Python - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of character access in a loop

What is the output of the following code snippet?

DSA Python

s = "hello"
result = []
for i in range(len(s)):
    if i % 2 == 0:
        result.append(s[i])
print(''.join(result))

A hlo

B el

C hello

D heo

💡 Hint

Look at characters at even indexes only.

The loop picks characters at indexes 0, 2, 4 which are 'h', 'l', 'o'. Joining them gives 'hlo'.

❓ Predict Output

intermediate

Output of negative indexing in string

What will be printed by this code?

DSA Python

s = "world"
print(s[-1] + s[-2] + s[-5])

A dlo

B dlw

C dwl

D wrd

💡 Hint

Negative indexes count from the end starting at -1.

s[-1] is 'd', s[-2] is 'l', s[-5] is 'w'. Concatenated: 'dlw'.

🔧 Debug

advanced

Identify the error in string character access

What error does this code raise when executed?

DSA Python

s = "data"
for i in range(len(s)+1):
    print(s[i])

A IndexError

B TypeError

C SyntaxError

D No error, prints all characters

💡 Hint

Check the range and valid indexes for string s.

The loop tries to access s[4] which is out of range for string of length 4, causing IndexError.

❓ Predict Output

advanced

Output of slicing with step in string

What is the output of this code?

DSA Python

s = "algorithm"
print(s[1:8:2])

A lorm

B lghm

C lgih

D loih

💡 Hint

Slice from index 1 to 7 with step 2.

Indexes 1,3,5,7 correspond to 'l', 'r', 'i', 'h'. Joining gives 'lrih'.

🧠 Conceptual

expert

Count of unique characters accessed in loop

Consider the code below. How many unique characters are printed?

DSA Python

s = "abracadabra"
seen = set()
for i in range(len(s)):
    if s[i] not in seen:
        print(s[i], end='')
        seen.add(s[i])

A 6

B 7

C 5

D 8

💡 Hint

Count distinct characters in the string.

The unique characters are 'a', 'b', 'r', 'c', 'd'. Counting carefully, there are 5 unique letters but the code prints them as they appear first time. The string has 'a','b','r','c','d' only 5 unique letters, but the code prints them once each, so 5 characters printed.