Selection Sort Algorithm in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to swap two elements in the array.

DSA C

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

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

Atemp

Bb

C0

Da

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning '*a' to '*b' instead of using the temporary variable.

Using the wrong variable name in the swap.

The variable 'temp' temporarily holds the value of '*a' so we can assign '*b' to '*a' and then assign 'temp' to '*b' to complete the swap.

2fill in blank

medium

Complete the code to find the index of the minimum element in the unsorted part of the array.

DSA C

int minIndex = i;
for (int j = i + 1; j < n; j++) {
    if (arr[j] [1] arr[minIndex]) {
        minIndex = j;
    }
}

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

A>

B<

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '<' which finds the maximum instead of minimum.

Using '==' which does not update the minimum index.

We compare if arr[j] is less than arr[minIndex] to find the smallest element's index.

3fill in blank

hard

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

DSA C

for (int i = 0; i [1] n - 1; i++) {
    // selection sort steps
}

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

A<

B<=

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' causes the loop to run one extra time and may cause errors.

Using '>' or '>=' causes the loop to never run.

The loop should run while i is less than n - 1 to avoid going out of bounds.

4fill in blank

hard

Fill both blanks to complete the selection sort inner loop and swap step.

DSA C

for (int j = i + 1; j [1] n; j++) {
    if (arr[j] [2] arr[minIndex]) {
        minIndex = j;
    }
}

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

A<

B>

C<=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>=' in the loop condition causes out of bounds errors.

Using '>' in the comparison finds the maximum instead of minimum.

The inner loop runs while j is less than n, and we check if arr[j] is less than arr[minIndex] to find the minimum.

5fill in blank

hard

Fill all three blanks to complete the selection sort function.

DSA C

void selectionSort(int arr[], int n) {
    for (int i = 0; i [1] n - 1; i++) {
        int minIndex = i;
        for (int j = i + 1; j [2] n; j++) {
            if (arr[j] [3] arr[minIndex]) {
                minIndex = j;
            }
        }
        swap(&arr[minIndex], &arr[i]);
    }
}

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

A<

B<=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' in outer loop causes extra iteration.

Using '>' in comparison finds maximum instead of minimum.

The outer loop runs while i < n-1, the inner loop runs while j < n, and the comparison uses '<' to find the minimum element.

Practice

1. What is the main idea behind the Selection Sort Algorithm?

easy

A. Divide the list and merge sorted parts

B. Swap adjacent elements if they are in wrong order

C. Repeatedly find the smallest element and move it to the front

D. Insert elements into their correct position one by one

Solution

1. Step 1: Understand selection sort process

   Selection sort finds the smallest element in the unsorted part and swaps it with the first unsorted element.

2. Step 2: Compare with other sorting methods

   Unlike bubble sort (swapping adjacent) or merge sort (divide and conquer), selection sort selects the minimum each time.

3. Final Answer:

   Repeatedly find the smallest element and move it to the front -> Option C

4. Quick Check:

   Selection sort = find minimum and swap [OK]

Hint: Selection sort picks smallest and swaps front [OK]

Common Mistakes:

• Confusing selection sort with bubble sort
• Thinking it sorts by inserting elements
• Believing it divides and merges lists

2. Which of the following is the correct syntax to swap two elements arr[i] and arr[min_idx] in C during selection sort?

easy

A. arr[i], arr[min_idx] = arr[min_idx], arr[i];

B. temp = arr[i]; arr[i] = arr[min_idx]; arr[min_idx] = temp;

C. swap(arr[i], arr[min_idx]);

D. arr[i] = arr[min_idx]; arr[min_idx] = arr[i];

Solution

1. Step 1: Understand swapping in C

   C does not have built-in swap; we use a temporary variable to hold one value during swap.

2. Step 2: Check each option

   temp = arr[i]; arr[i] = arr[min_idx]; arr[min_idx] = temp; uses a temp variable correctly. arr[i] = arr[min_idx]; arr[min_idx] = arr[i]; overwrites arr[i] before saving. swap(arr[i], arr[min_idx]); is invalid syntax in C. arr[i], arr[min_idx] = arr[min_idx], arr[i]; is Python syntax, not C.

3. Final Answer:

   temp = arr[i]; arr[i] = arr[min_idx]; arr[min_idx] = temp; -> Option B

4. Quick Check:

   Use temp variable to swap in C [OK]

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

Common Mistakes:

• Trying to swap without temp variable
• Using Python or other language syntax
• Overwriting values before saving

3. What will be the output array after the first pass of selection sort on arr = {29, 10, 14, 37, 13}?

medium

A. {10, 29, 14, 37, 13}

B. {29, 10, 14, 37, 13}

C. {13, 10, 14, 37, 29}

D. {10, 14, 29, 37, 13}

Solution

1. Step 1: Find minimum in entire array

   Minimum element is 10 at index 1.

2. Step 2: Swap minimum with first element

   Swap 29 (index 0) with 10 (index 1). Array becomes {10, 29, 14, 37, 13}.

3. Final Answer:

   {10, 29, 14, 37, 13} -> Option A

4. Quick Check:

   First pass swaps smallest to front [OK]

Hint: First pass swaps smallest element to front [OK]

Common Mistakes:

• Not swapping after finding minimum
• Swapping with wrong index
• Confusing first pass with full sort

4. Identify the error in this selection sort snippet and choose the fix:

for (int i = 0; i < n; i++) {
  int min_idx = i;
  for (int j = i + 1; j < n; j++) {
    if (arr[j] < arr[min_idx])
      min_idx = j;
  }
  arr[i] = arr[min_idx];
  arr[min_idx] = arr[i];
}

medium

A. Swap lines overwrite values; use a temp variable to swap

B. Change inner loop to start from j = 0

C. Remove inner loop; selection sort doesn't need it

D. Use arr[min_idx] = arr[j] instead of arr[min_idx] = arr[i]

Solution

1. Step 1: Analyze swap lines

   Lines arr[i] = arr[min_idx]; arr[min_idx] = arr[i]; overwrite arr[min_idx] with arr[i] after first assignment, losing original value.

2. Step 2: Correct swap method

   Use a temporary variable to hold arr[i], then assign arr[i] = arr[min_idx], then arr[min_idx] = temp to swap correctly.

3. Final Answer:

   Swap lines overwrite values; use a temp variable to swap -> Option A

4. Quick Check:

   Swap needs temp variable to avoid overwrite [OK]

Hint: Use temp variable to swap, not direct assignments [OK]

Common Mistakes:

• Swapping without temp variable
• Changing loop start incorrectly
• Removing necessary inner loop

5. Given the array arr = {64, 25, 12, 22, 11}, after fully sorting it using selection sort, what is the final sorted array?

hard

A. {64, 25, 12, 22, 11}

B. {11, 22, 12, 25, 64}

C. {25, 11, 12, 22, 64}

D. {11, 12, 22, 25, 64}

Solution

1. Step 1: Perform selection sort passes

   Pass 1: min=11, swap with 64 -> {11,25,12,22,64}
   Pass 2: min=12, swap with 25 -> {11,12,25,22,64}
   Pass 3: min=22, swap with 25 -> {11,12,22,25,64}
   Pass 4: min=25, no swap needed -> {11,12,22,25,64}

2. Step 2: Confirm final sorted array

   After all passes, array is sorted ascending: {11, 12, 22, 25, 64}.

3. Final Answer:

   {11, 12, 22, 25, 64} -> Option D

4. Quick Check:

   Selection sort fully sorts ascending [OK]

Hint: Selection sort sorts ascending by swapping minimum each pass [OK]

Common Mistakes:

• Stopping after first pass
• Not swapping correctly
• Mixing up element positions