Merge Sort Algorithm in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find the middle index for splitting the array.

DSA C++

int mid = (left [1] right) / 2;

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A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction instead of addition.

Using multiplication which is incorrect here.

The middle index is found by adding left and right, then dividing by 2.

2fill in blank

medium

Complete the code to merge two sorted halves by comparing elements.

DSA C++

if (leftArr[i] [1] rightArr[j]) { merged[k++] = leftArr[i++]; } else { merged[k++] = rightArr[j++]; }

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

A<=

B<

C>=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using > instead of < causes wrong order.

Using <= or >= can cause duplicates or errors.

We pick the smaller element first, so we use < to compare.

3fill in blank

hard

Fix the error in the recursive call to sort the right half.

DSA C++

mergeSort(arr, [1], right);

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

Amid

Bright - 1

Cmid + 1

Dleft

Attempts:

3 left

💡 Hint

Common Mistakes

Using mid instead of mid + 1 causes overlap.

Using right - 1 misses the last element.

The right half starts from mid + 1 to right.

4fill in blank

hard

Fill both blanks to copy remaining elements from left and right arrays after merging.

DSA C++

while (i < n1) merged[k++] = leftArr[1]; while (j < n2) merged[k++] = rightArr[2];

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

A[i++]

B[j++]

C[k++]

D[i]

Attempts:

3 left

💡 Hint

Common Mistakes

Using [k++] causes wrong indexing.

Not incrementing i or j causes infinite loops.

We copy remaining elements by using i++ and j++ to move indices.

5fill in blank

hard

Fill all three blanks to copy merged array back to original array.

DSA C++

for (int idx = 0; idx < n1 + n2; idx++) arr[1] = merged[2]; [3]

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A[left + idx]

B[idx]

C// end of copying

D[idx + left]

Attempts:

3 left

💡 Hint

Common Mistakes

Using arr[idx] overwrites wrong part of array.

Missing the comment line is okay but less clear.

We copy merged elements back starting at left index. The comment marks end of copying.