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

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code snippet?

Given an array where every element repeats twice except one, find the unique element using XOR.

DSA C

int arr[] = {2, 3, 5, 4, 5, 3, 4};
int n = 7;
int unique = 0;
for (int i = 0; i < n; i++) {
    unique ^= arr[i];
}
printf("%d\n", unique);

A 5

B 2

C 3

D 4

💡 Hint

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

All numbers except 2 appear twice, so XOR cancels them out leaving 2.

❓ Predict Output

intermediate

What is the output of this XOR operation on the array?

Find the unique element in the array using XOR.

DSA C

int arr[] = {10, 14, 10, 14, 15};
int n = 5;
int unique = 0;
for (int i = 0; i < n; i++) {
    unique ^= arr[i];
}
printf("%d\n", unique);

A 15

B 10

C 0

D 14

💡 Hint

XOR cancels pairs, leaving the unique number.

10 and 14 appear twice, so XOR cancels them, leaving 15.

❓ Predict Output

advanced

What is the output of this code with negative numbers?

Find the unique element using XOR in an array with negative and positive integers.

DSA C

int arr[] = {-1, -2, -2, -1, -3};
int n = 5;
int unique = 0;
for (int i = 0; i < n; i++) {
    unique ^= arr[i];
}
printf("%d\n", unique);

A -3

B -1

C -2

D 0

💡 Hint

XOR works with negative numbers as well.

Pairs cancel out, leaving -3 as unique.

🧠 Conceptual

advanced

Why does XOR help find the unique element in an array where all others repeat twice?

Choose the best explanation for why XOR operation can find the only non-repeating element.

A XOR sorts the array and picks the middle element as unique.

B XOR adds all numbers together and divides by two to find the unique number.

C XOR multiplies all numbers and the unique number remains after division.

D XOR of a number with itself is zero, so pairs cancel out, leaving the unique number.

💡 Hint

Think about how XOR behaves with identical numbers.

XOR of two identical numbers is zero, so all pairs cancel out leaving the unique number.

❓ Predict Output

expert

What is the output of this code with a large array?

Find the unique element using XOR in a large array where all elements except one repeat twice.

DSA C

int arr[] = {100, 200, 300, 100, 200, 400, 300, 500, 400};
int n = 9;
int unique = 0;
for (int i = 0; i < n; i++) {
    unique ^= arr[i];
}
printf("%d\n", unique);

A 300

B 400

C 500

D 100

💡 Hint

All numbers except one appear twice.

Pairs cancel out, leaving 500 as unique.