Find the Only Non Repeating Element Using XOR in DSA C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does XOR operation do when applied between two identical bits?

XOR of two identical bits is 0. For example, 1 ^ 1 = 0 and 0 ^ 0 = 0.

beginner

Why does XOR help find the only non-repeating element in an array where every other element repeats twice?

Because XOR of a number with itself is 0, all repeating elements cancel out, leaving only the non-repeating element after XORing all elements.

beginner

What is the initial value of the variable used to store XOR results when finding the non-repeating element?

The initial value should be 0 because XOR with 0 returns the number itself, so it doesn't affect the result.

beginner

Given the array [2, 3, 2, 4, 4], what is the only non-repeating element found using XOR?

The only non-repeating element is 3 because XORing all elements results in 3.

beginner

Write the time complexity of finding the only non-repeating element using XOR in an array of size n.

The time complexity is O(n) because we need to XOR all elements once.

What is the result of XORing a number with 0?

A The number itself

B 0

C 1

D Undefined

XOR of any number with 0 returns the number itself.

If every element except one appears twice in an array, what does XORing all elements give?

A Sum of all elements

B Product of all elements

C 0

D The non-repeating element

XOR cancels out pairs of identical elements, leaving the unique element.

What is the initial value to start XOR accumulation when finding the unique element?

A 1

B 0

C First element of array

D Array length

Starting with 0 ensures XOR operation works correctly without affecting results.

What is the time complexity of the XOR method to find the unique element in an array?

A O(n^2)

B O(n log n)

C O(n)

D O(1)

We XOR all elements once, so time complexity is linear O(n).

Which of the following is true about XOR operation?

A XOR is commutative and associative

B XOR of a number with itself is the number

C XOR of any number with 1 is 0

D XOR always increases the number

XOR is both commutative (order doesn't matter) and associative (grouping doesn't matter).

Explain how XOR operation helps find the only non-repeating element in an array where every other element repeats twice.

Think about how pairs of numbers behave with XOR.

Describe the steps and code logic to find the only non-repeating element using XOR in C.

Focus on how XOR accumulates the answer.