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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to swap elements between two arrays.

DSA C#

if (arr1[i] > arr2[0]) {
    int temp = arr1[i];
    arr1[i] = arr2[[1]];
    arr2[0] = temp;
}

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

Aarr2.Length - 1

Bi

Carr1.Length - 1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping with wrong index in arr2 causes incorrect order.

Using arr1.Length - 1 instead of 0 for arr2 index.

We swap arr1[i] with arr2[0] to maintain order before sorting arr2.

2fill in blank

medium

Complete the code to sort the second array after swapping.

DSA C#

for (int i = 1; i < arr2.Length; i++) {
    int key = arr2[i];
    int j = i - 1;
    while (j >= 0 && arr2[j] > [1]) {
        arr2[j + 1] = arr2[j];
        j--;
    }
    arr2[j + 1] = key;
}

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

Akey

Barr2[i]

Carr2[j]

Darr1[i]

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with arr2[i] instead of key causes wrong sorting.

Using arr1[i] which is unrelated here.

We compare arr2[j] with key to insert key in the correct position.

3fill in blank

hard

Fix the error in the loop condition to merge arrays correctly.

DSA C#

for (int i = 0; i < [1]; i++) {
    if (arr1[i] > arr2[0]) {
        int temp = arr1[i];
        arr1[i] = arr2[0];
        arr2[0] = temp;
        // Sort arr2
        // ...
    }
}

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

Aarr2.Length

Barr1.Length + arr2.Length

Carr1.Length

Darr1.Length - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using arr2.Length causes index out of range or incomplete merging.

Using arr1.Length - 1 misses the last element.

The loop should run through all elements of arr1 to compare and swap.

4fill in blank

hard

Fill both blanks to complete the merge function without extra space.

DSA C#

public static void Merge(int[] arr1, int[] arr2) {
    int n = arr1.Length;
    int m = arr2.Length;
    for (int i = 0; i < [1]; i++) {
        if (arr1[i] > arr2[0]) {
            int temp = arr1[i];
            arr1[i] = arr2[0];
            arr2[0] = temp;
            // Sort arr2
            int first = arr2[0];
            int k;
            for (k = 1; k < [2] && arr2[k] < first; k++) {
                arr2[k - 1] = arr2[k];
            }
            arr2[k - 1] = first;
        }
    }
}

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

An

Bm

Cn + m

Dm - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong lengths causes index errors or incomplete sorting.

Mixing arr1 and arr2 lengths in loops.

The outer loop runs for all elements in arr1 (n). The inner loop sorts arr2 up to its length (m).

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that counts elements greater than zero.

DSA C#

var result = new Dictionary<string, int> {
    {"positiveCount", arr1.Count(x => x [1] 0) + arr2.Count(x => x [2] 0)},
    {"maxValue", Math.Max(arr1.Max(), arr2.Max())},
    {"minValue", Math.Min(arr1.Min(), arr2.Min())}
};

// Print result
foreach (var kvp in result) {
    Console.WriteLine($"{kvp.Key}: {kvp.Value}");
}

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

A>

B<

C>=

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '<=' counts wrong elements.

Confusing operators in Count conditions.

We count elements greater than zero using '>'. The max and min values use standard functions.

Practice

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

easy

A. Create a new array to hold merged elements

B. Combine both arrays into one sorted sequence without using extra memory

C. Copy elements from one array to another without sorting

D. Sort each array separately using extra space

Solution

1. Step 1: Understand the problem requirement

   The task is to merge two sorted arrays so that the combined elements remain sorted, but without using any extra space like a new array.

2. Step 2: Identify the correct approach

   We must rearrange elements within the given arrays themselves to maintain sorted order without additional memory.

3. Final Answer:

   Combine both arrays into one sorted sequence without using extra memory -> Option B

4. Quick Check:

   Merge without extra space = Combine in place [OK]

Hint: Merge by swapping elements between arrays without extra space [OK]

Common Mistakes:

• Assuming extra space is allowed
• Sorting arrays separately without merging
• Creating a new array for merged result

2. Which of the following C# code snippets correctly swaps elements between two arrays without extra space?

easy

A. arr1[i] = arr1[i] + arr2[j]; arr2[j] = arr1[i] - arr2[j]; arr1[i] = arr1[i] - arr2[j];

B. arr1[i] = arr2[j]; arr2[j] = arr1[i];

C. if (arr1[i] > arr2[j]) { int temp = arr1[i]; arr1[i] = arr2[j]; arr2[j] = temp; }

D. int temp = arr2[j]; arr2[j] = arr1[i]; arr1[i] = temp + 1;

Solution

1. Step 1: Check swapping logic correctness

   if (arr1[i] > arr2[j]) { int temp = arr1[i]; arr1[i] = arr2[j]; arr2[j] = temp; } uses a temporary variable to swap values correctly without losing data.

2. Step 2: Analyze other options for errors

   arr1[i] = arr2[j]; arr2[j] = arr1[i]; overwrites arr2[j] before saving arr1[i], losing original value. arr1[i] = arr1[i] + arr2[j]; arr2[j] = arr1[i] - arr2[j]; arr1[i] = arr1[i] - arr2[j]; uses arithmetic swap but can cause overflow and is less safe. int temp = arr2[j]; arr2[j] = arr1[i]; arr1[i] = temp + 1; incorrectly adds 1 during swap, changing values.

3. Final Answer:

   if (arr1[i] > arr2[j]) { int temp = arr1[i]; arr1[i] = arr2[j]; arr2[j] = temp; } -> Option C

4. Quick Check:

   Temporary variable swap = Correct swap [OK]

Hint: Use a temp variable to swap safely in C# [OK]

Common Mistakes:

• Overwriting values without temp variable
• Using unsafe arithmetic swaps
• Altering values unintentionally during swap

3. What will be the content of arrays after running this code?

int[] arr1 = {1, 5, 9, 10, 15, 20};
int[] arr2 = {2, 3, 8, 13};
int n = arr1.Length, m = arr2.Length;
for (int i = 0; i < n; i++) {
  if (arr1[i] > arr2[0]) {
    int temp = arr1[i];
    arr1[i] = arr2[0];
    arr2[0] = temp;
    int first = arr2[0];
    int k;
    for (k = 1; k < m && arr2[k] < first; k++) {
      arr2[k - 1] = arr2[k];
    }
    arr2[k - 1] = first;
  }
}

medium

A. arr1 = [1, 2, 3, 5, 9, 10], arr2 = [8, 13, 15, 20]

B. arr1 = [1, 3, 5, 8, 9, 10], arr2 = [2, 13, 15, 20]

C. arr1 = [1, 2, 5, 8, 9, 10], arr2 = [3, 13, 15, 20]

D. arr1 = [1, 2, 3, 5, 8, 9], arr2 = [10, 13, 15, 20]

Solution

1. Step 1: Trace the swapping and insertion in arr2

   For each element in arr1, if it is greater than arr2[0], swap and then insert arr2[0] in sorted order in arr2. This pushes larger elements to arr2.

2. Step 2: Final arrays after all iterations

   After all swaps and insertions, arr1 becomes [1, 2, 3, 5, 8, 9] and arr2 becomes [10, 13, 15, 20].

3. Final Answer:

   arr1 = [1, 2, 3, 5, 8, 9], arr2 = [10, 13, 15, 20] -> Option D

4. Quick Check:

   In-place merge with insertion sort = arr1 and arr2 sorted [OK]

Hint: Swap if arr1[i] > arr2[0], then insert arr2[0] sorted [OK]

Common Mistakes:

• Not inserting arr2[0] correctly after swap
• Overwriting arr2 elements incorrectly
• Confusing array indices during insertion

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;
    int first = arr2[0];
    int k = 1;
    while (k < m && arr2[k] < first) {
      arr2[k - 1] = arr2[k];
      k++;
    }
    arr2[k] = first;
  }
}

medium

A. The insertion index in arr2 is incorrect; should be arr2[k - 1] = first

B. The swap logic between arr1[i] and arr2[0] is wrong

C. The loop should run from i = 1 instead of 0

D. The condition arr2[k] < first should be arr2[k] > first

Solution

1. Step 1: Analyze insertion logic in arr2

   The code shifts elements left to make space for 'first'. The correct insertion index after shifting is k - 1, not k.

2. Step 2: Identify the error impact

   Assigning arr2[k] = first overwrites the next element incorrectly, causing wrong order.

3. Final Answer:

   The insertion index in arr2 is incorrect; should be arr2[k - 1] = first -> Option A

4. Quick Check:

   Correct insertion index = k - 1 [OK]

Hint: Insert shifted element at k-1 index after loop ends [OK]

Common Mistakes:

• Using wrong index for insertion after shifting
• Incorrect swap logic
• Wrong loop start index

5. Given two sorted arrays:
arr1 = [1, 4, 7, 8, 10]
arr2 = [2, 3, 9]
How would you merge them without extra space so that after merging, arr1 contains the first 5 smallest elements and arr2 contains the remaining sorted elements? Choose the correct final arrays.

hard

A. arr1 = [1, 2, 3, 4, 7], arr2 = [8, 9, 10]

B. arr1 = [1, 3, 4, 7, 8], arr2 = [2, 9, 10]

C. arr1 = [1, 2, 4, 7, 8], arr2 = [3, 9, 10]

D. arr1 = [1, 2, 3, 4, 8], arr2 = [7, 9, 10]

Solution

1. Step 1: Compare and swap elements between arr1 and arr2

   Start from beginning of arr1, if arr1[i] > arr2[0], swap and then insert arr2[0] in sorted order in arr2.

2. Step 2: After all swaps and insertions

   arr1 becomes [1, 2, 3, 4, 7] and arr2 becomes [8, 9, 10], maintaining sorted order without extra space.

3. Final Answer:

   arr1 = [1, 2, 3, 4, 7], arr2 = [8, 9, 10] -> Option A

4. Quick Check:

   In-place merge keeps first array smallest elements [OK]

Hint: Swap if arr1[i] > arr2[0], then insert arr2[0] sorted [OK]

Common Mistakes:

• Not maintaining sorted order after swap
• Incorrect insertion in second array
• Assuming extra space is allowed