Find the Only Non Repeating Element Using XOR in DSA Python - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code using XOR to find the unique element?

Given the list arr = [2, 3, 5, 4, 5, 3, 4], what will be printed after running the code below?

DSA Python

arr = [2, 3, 5, 4, 5, 3, 4]
unique = 0
for num in arr:
    unique ^= num
print(unique)

A 0

B 4

C 5

D 2

💡 Hint

XOR of a number with itself is 0, and XOR with 0 is the number itself.

All numbers except 2 appear twice. XOR cancels out duplicates, leaving 2 as the unique element.

❓ Predict Output

intermediate

What is the output of this XOR code with negative numbers?

Given arr = [-1, -2, -2, -1, -3], what will the code print?

DSA Python

arr = [-1, -2, -2, -1, -3]
unique = 0
for num in arr:
    unique ^= num
print(unique)

A -3

B -1

C 0

D -2

💡 Hint

XOR works the same with negative numbers as with positive.

Pairs cancel out, leaving -3 as the unique number.

🔧 Debug

advanced

What error does this code raise?

What error will this code raise when trying to find the unique element using XOR?

DSA Python

arr = [1, 2, 2, 1, '3']
unique = 0
for num in arr:
    unique ^= num
print(unique)

A No error, prints 3

B SyntaxError

C TypeError

D ValueError

💡 Hint

XOR operator requires both operands to be integers.

The string '3' cannot be XORed with an integer, causing a TypeError.

🧠 Conceptual

advanced

How many times is the XOR operation applied in this code?

Given an array of length n, how many XOR operations does the code below perform?

DSA Python

arr = [some list of length n]
unique = 0
for num in arr:
    unique ^= num
print(unique)

A n

B n-1

C n+1

D 1

💡 Hint

The XOR happens once per element in the loop.

The loop runs n times, applying XOR each time.

🚀 Application

expert

What is the unique element after XOR operations on this large array?

Given the array arr = [10, 14, 10, 14, 20, 30, 20], what is the unique element found by XOR?

DSA Python

arr = [10, 14, 10, 14, 20, 30, 20]
unique = 0
for num in arr:
    unique ^= num
print(unique)

A 20

B 30

C 14

D 10

💡 Hint

Pairs cancel out, leaving the unique number.

All numbers except 30 appear twice, so 30 is the unique element.