Find the Only Non Repeating Element Using XOR in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the result variable to zero.

DSA Typescript

let result = [1];

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

Aundefined

B1

Cnull

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing result with 1 or null instead of 0.

We start with zero because XOR with zero returns the other number unchanged.

2fill in blank

medium

Complete the for loop to iterate over all elements in the array 'arr'.

DSA Typescript

for (let i = 0; i [1] arr.length; i++) {
  result ^= arr[i];
}

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

A<

B<=

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= causes index out of range error.

The loop should run while i is less than arr.length to avoid out-of-bounds access.

3fill in blank

hard

Fix the error in the XOR operation inside the loop.

DSA Typescript

result [1] arr[i];

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

A+=

B-=

C^=

D*=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+=' or other arithmetic operators instead of '^='.

The XOR assignment operator '^=' is used to combine bits correctly.

4fill in blank

hard

Fill both blanks to complete the function signature and return statement.

DSA Typescript

function findUnique(arr: number[]): number {
  let result = 0;
  for (let i = 0; i < arr.length; i++) {
    result [1] arr[i];
  }
  return [2];
}

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

A^=

B+=

Cresult

Darr[i]

Attempts:

3 left

💡 Hint

Common Mistakes

Returning arr[i] or using '+=' instead of '^='.

Use '^=' to XOR each element with result, then return result.

5fill in blank

hard

Fill all three blanks to complete the code that calls the function and prints the unique element.

DSA Typescript

const numbers = [2, 3, 5, 4, 5, 3, 4];
const unique = [1](numbers);
console.[2]("Unique element is:", [3]);

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

AfindUnique

Blog

Cunique

Dprint

Attempts:

3 left

💡 Hint

Common Mistakes

Using console.print or wrong variable names.

Call findUnique with numbers, then log the unique variable to console.

Practice

1. What does the XOR operation do when applied between two identical numbers?

easy

A. It returns 1

B. It returns the number itself

C. It returns 0

D. It returns the sum of the numbers

Solution

1. Step 1: Understand XOR property for identical numbers

   XOR of a number with itself always results in 0 because bits cancel out.

2. Step 2: Apply XOR to example

   For example, 5 XOR 5 = 0.

3. Final Answer:

   It returns 0 -> Option C

4. Quick Check:

   X XOR X = 0 [OK]

Hint: XOR of same numbers is always zero [OK]

Common Mistakes:

• Thinking XOR returns the number itself
• Confusing XOR with OR or AND
• Assuming XOR sums the numbers

2. Which of the following TypeScript code snippets correctly initializes a variable to zero for XOR operation?

easy

A. let result = 1;

B. let result = 0;

C. let result = null;

D. let result = undefined;

Solution

1. Step 1: Identify correct initial value for XOR

   For XOR operations, starting with 0 is correct because 0 XOR any number returns that number.

2. Step 2: Check code snippets

   Only let result = 0; correctly initializes for XOR accumulation.

3. Final Answer:

   let result = 0; -> Option B

4. Quick Check:

   Initial XOR value = 0 [OK]

Hint: Start XOR with zero to keep numbers unchanged [OK]

Common Mistakes:

• Starting XOR with 1 instead of 0
• Using null or undefined which cause errors
• Not initializing the variable

3. What is the output of the following TypeScript code?

const arr = [2, 3, 2, 4, 3];
let result = 0;
for (const num of arr) {
  result ^= num;
}
console.log(result);

medium

A. 3

B. 0

C. 2

D. 4

Solution

1. Step 1: XOR all elements in the array

   Calculate stepwise: 0 XOR 2 = 2, 2 XOR 3 = 1, 1 XOR 2 = 3, 3 XOR 4 = 7, 7 XOR 3 = 4.

2. Step 2: Identify the non-repeating element

   All repeating numbers cancel out, leaving 4 as the only non-repeating element.

3. Final Answer:

   4 -> Option D

4. Quick Check:

   Result after XOR = 4 [OK]

Hint: XOR all numbers; duplicates cancel out [OK]

Common Mistakes:

• Not XORing all elements
• Confusing output with last element
• Assuming sum instead of XOR

4. Identify the error in this TypeScript code that tries to find the only non-repeating element using XOR:

const arr = [1, 2, 1, 3, 2];
let result;
for (let i = 0; i < arr.length; i++) {
  result ^= arr[i];
}
console.log(result);

medium

A. Variable 'result' is not initialized

B. Loop condition is incorrect

C. XOR operator is used wrongly

D. Array is empty

Solution

1. Step 1: Check variable initialization

   The variable 'result' is declared but not initialized, so it is undefined initially.

2. Step 2: Understand XOR with undefined

   XOR with undefined causes NaN or runtime error; it must start at 0.

3. Final Answer:

   Variable 'result' is not initialized -> Option A

4. Quick Check:

   Initialize result = 0 before XOR loop [OK]

Hint: Always initialize XOR accumulator to zero [OK]

Common Mistakes:

• Forgetting to initialize result
• Assuming undefined XOR number works
• Incorrect loop boundaries

5. Given an array where every element repeats twice except one element which repeats thrice, can XOR alone find the unique element? Why?

const arr = [5, 5, 5, 7, 7, 8, 8];

hard

A. No, XOR fails because it only cancels pairs, not triples

B. Yes, XOR works because duplicates cancel out

C. Yes, but only if array is sorted

D. No, XOR works only for arrays with all unique elements

Solution

1. Step 1: Understand XOR behavior with odd counts

   XOR cancels even appearances (like twice) to 0, but leaves the result of odd appearances (like thrice: x ^ x ^ x = 0, not x).

2. Step 2: Analyze the given array

   5 appears thrice (odd), 7 and 8 twice (even); XOR of all yields 0, so XOR alone cannot find the unique element repeated thrice.

3. Final Answer:

   No, XOR fails because it only cancels pairs, not triples -> Option A

4. Quick Check:

   XOR fails to find element repeated thrice [OK]

Hint: XOR cancels pairs, fails for triples [OK]

Common Mistakes:

• Thinking XOR works for triples
• Believing sorting is required for XOR
• Confusing XOR with requiring exactly one unique