Merge Two Sorted Arrays Without Extra Space in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to swap two integers using pointers.

DSA C

void swap(int *a, int *b) {
    int temp = *a;
    *a = [1];
    *b = temp;
}

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

Aa

B*a

Ctemp

D*b

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable names instead of dereferencing pointers.

To swap values, assign the value pointed by b to the location pointed by a.

2fill in blank

medium

Complete the condition to check if the first array element is greater than the second array element.

DSA C

if (arr1[i] [1] arr2[j]) {
    // swap logic
}

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

A>

B<

C==

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than instead of greater than.

We swap when the element in arr1 is greater than the element in arr2.

3fill in blank

hard

Fix the error in the loop condition to iterate over the first array.

DSA C

for (int i = 0; i [1] n; i++) {
    // processing
}

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

A>

B<

C>=

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using > or >= causes no iterations or errors.

The loop should run while i is less than n to cover all elements from 0 to n-1.

4fill in blank

hard

Fill both blanks to complete the nested loops for merging arrays.

DSA C

for (int i = 0; i [1] n; i++) {
    for (int j = 0; j [2] m; j++) {
        if (arr1[i] > arr2[j]) {
            swap(&arr1[i], &arr2[j]);
        }
    }
}

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 errors.

Both loops should run from 0 to less than their respective sizes to cover all elements.

5fill in blank

hard

Fill all three blanks to complete the function that merges two sorted arrays without extra space.

DSA C

void merge(int arr1[], int arr2[], int n, int m) {
    for (int i = 0; i [1] n; i++) {
        if (arr1[i] > arr2[0]) {
            [2](&arr1[i], &arr2[0]);
            int first = arr2[0];
            int k;
            for (k = 1; k [3] m && arr2[k] < first; k++) {
                arr2[k - 1] = arr2[k];
            }
            arr2[k - 1] = first;
        }
    }
}

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

A<

Bswap

C<=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using > instead of < in loops.

Forgetting to swap elements.

The outer loop runs while i < n. We swap arr1[i] and arr2[0] if needed. The inner loop shifts elements in arr2 while k < m and arr2[k] < first.

Practice

1. What is the main goal when merging two sorted arrays without extra space?

easy

A. Combine both arrays into one sorted array without using extra memory

B. Sort each array separately using extra memory

C. Copy elements from one array to another without sorting

D. Create a new array to hold merged elements

Solution

1. Step 1: Understand the problem requirement

   The task is to merge two sorted arrays into a single sorted sequence without using extra space, meaning no additional arrays or large buffers.

2. Step 2: Identify the correct approach

   We must rearrange elements within the given arrays to maintain sorted order without allocating extra memory.

3. Final Answer:

   Combine both arrays into one sorted array without using extra memory -> Option A

4. Quick Check:

   Merge without extra space = Combine in place [OK]

Hint: Merge by swapping elements, no extra array needed [OK]

Common Mistakes:

• Thinking extra array is allowed
• Sorting arrays separately without merging
• Copying elements without sorting

2. Which of the following C code snippets correctly declares two sorted arrays for merging without extra space?

easy

A. int arr1[] = (1, 3, 5); int arr2[] = (2, 4, 6);

B. int arr1 = {1, 3, 5}; int arr2 = {2, 4, 6};

C. int arr1[] = [1, 3, 5]; int arr2[] = [2, 4, 6];

D. int arr1[] = {1, 3, 5}; int arr2[] = {2, 4, 6};

Solution

1. Step 1: Check array declaration syntax in C

   Arrays in C are declared using curly braces {} with type and square brackets [].

2. Step 2: Validate each option

   int arr1[] = {1, 3, 5}; int arr2[] = {2, 4, 6}; uses correct syntax: int arr[] = {elements}; Options A, B, and D use invalid syntax for arrays in C.

3. Final Answer:

   int arr1[] = {1, 3, 5}; int arr2[] = {2, 4, 6}; -> Option D

4. Quick Check:

   C arrays use {} for initialization [OK]

Hint: Use curly braces {} to initialize arrays in C [OK]

Common Mistakes:

• Using parentheses () or square brackets [] for initialization
• Missing data type or brackets
• Assigning arrays without braces

3. Given two sorted arrays:
arr1 = {1, 4, 7, 8, 10}
arr2 = {2, 3, 9}
After merging without extra space, what will be the content of arr1?

medium

A. [1, 2, 3, 4, 8]

B. [1, 2, 3, 4, 7]

C. [1, 2, 3, 7, 8]

D. [1, 3, 4, 7, 8]

Solution

1. Step 1: Understand merging without extra space

   We merge by comparing elements and swapping to keep smallest elements in arr1.

2. Step 2: Merge process

   Initial arr1: [1,4,7,8,10], arr2: [2,3,9]
   Compare 10 (arr1 last) and 2 (arr2 first), swap -> arr1: [1,4,7,8,2], arr2: [10,3,9]
   Sort arr2: [3,9,10]
   Repeat swaps and sorts until arr1 holds smallest 5 elements:
   Final arr1: [1,2,3,4,7]

3. Final Answer:

   [1, 2, 3, 4, 7] -> Option B

4. Quick Check:

   Smallest 5 elements in arr1 after merge = [1,2,3,4,7] [OK]

Hint: Keep smallest elements in first array by swapping [OK]

Common Mistakes:

• Not sorting arr2 after swaps
• Assuming arr1 remains unchanged
• Mixing elements without sorting

4. Identify the error in this code snippet for merging two sorted arrays without extra space:

for (int i = 0; i < n; i++) {
  if (arr1[i] > arr2[0]) {
    int temp = arr1[i];
    arr1[i] = arr2[0];
    arr2[0] = temp;
    sort(arr2, arr2 + m);
  }
}

medium

A. Using sort() without including <algorithm> header

B. Swapping elements incorrectly between arrays

C. Sorting arr2 inside the loop causes inefficiency

D. Loop should run from 0 to m instead of n

Solution

1. Step 1: Analyze the loop and sorting

   The code swaps elements and sorts arr2 inside the loop for every iteration.

2. Step 2: Identify inefficiency

   Sorting arr2 in every iteration is costly and inefficient; better to optimize sorting or use a different approach.

3. Final Answer:

   Sorting arr2 inside the loop causes inefficiency -> Option C

4. Quick Check:

   Sorting inside loop = inefficient [OK]

Hint: Avoid sorting inside loops for better performance [OK]

Common Mistakes:

• Ignoring performance impact of repeated sorting
• Confusing array sizes for loop limits
• Assuming swap logic is incorrect

5. You have two sorted arrays:
arr1 = {1, 5, 9, 10, 15, 20}
arr2 = {2, 3, 8, 13}
Using the gap method to merge without extra space, what is the final state of arr2 after merging?

hard

A. [10, 13, 15, 20]

B. [8, 9, 10, 15]

C. [8, 13, 15, 20]

D. [9, 10, 13, 15]

Solution

1. Step 1: Understand the gap method

   The gap method compares elements at a gap distance and swaps if out of order, reducing gap until 1.

2. Step 2: Apply gap method to arrays

   Initial arr1: [1,5,9,10,15,20], arr2: [2,3,8,13]
   After merging, arr1 holds smallest elements: [1,2,3,5,8,9]
   arr2 holds remaining elements: [10,13,15,20]

3. Step 3: Final arr2 state

   arr2 after merge is [10, 13, 15, 20].

4. Final Answer:

   [10, 13, 15, 20] -> Option A

5. Quick Check:

   Gap method final arr2 = [10, 13, 15, 20] [OK]

Hint: Gap method sorts by comparing distant elements [OK]

Common Mistakes:

• Confusing final positions of elements in arr2
• Assuming arr2 remains unchanged
• Misapplying gap calculation