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++

int temp = arr[i];
arr[i] = arr[[1]];
arr[[1]] = temp;

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

Aj

Bi

CminIndex

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping with the wrong index like j or i itself.

Forgetting to use a temporary variable for swapping.

We swap the element at index i with the element at the minIndex to place the smallest element found at the correct position.

2fill in blank

medium

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

DSA C++

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

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

AminIndex

Bi

Cj

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with arr[i] instead of arr[minIndex].

Using j as the index to compare with itself.

We compare arr[j] with arr[minIndex] to find the smallest element's index in the unsorted part.

3fill in blank

hard

Fix the error in the loop condition to avoid going out of array bounds.

DSA C++

for (int i = 0; i < [1]; i++) {
    // selection sort logic
}

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

An

Bn / 2

Cn + 1

Dn - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using i < n causes unnecessary iteration.

Using i < n + 1 causes out of bounds error.

The outer loop runs until n - 1 because the last element will already be sorted after previous passes.

4fill in blank

hard

Fill both blanks to complete the inner loop and update the minimum index correctly.

DSA C++

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

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

Ai + 1

Bi

CminIndex

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Starting inner loop from 0 or i instead of i + 1.

Comparing with arr[i] instead of arr[minIndex].

The inner loop starts from i + 1 to check the unsorted part, and we compare with arr[minIndex] to find the smallest element.

5fill in blank

hard

Fill all three blanks to complete the code that populates a std::map mapping elements greater than 10 to their indices.

DSA C++

std::map<int, int> result;
for (int i = 0; i < arr.size(); i++) {
    if (arr[i] [3] 10) {
        result[[1]] = [2];
    }
}

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

Aarr[i]

Bi

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong comparison operator.

Swapping key and value in the map.

We map each element arr[i] to its index i only if the element is greater than 10.

Practice

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

easy

A. Divide the array into halves and sort each half recursively

B. Swap adjacent elements if they are in wrong order

C. Repeatedly find the minimum element and place it at the beginning

D. Use a heap data structure to sort elements

Solution

1. Step 1: Understand Selection Sort process

   Selection Sort works by finding the smallest element in the unsorted part and swapping it with the first unsorted element.

2. Step 2: Compare with other sorting methods

   Unlike swapping adjacent elements or dividing arrays, Selection Sort directly selects the minimum element each time.

3. Final Answer:

   Repeatedly find the minimum element and place it at the beginning -> Option C

4. Quick Check:

   Selection Sort = Find minimum and swap [OK]

Hint: Selection Sort picks minimum each pass [OK]

Common Mistakes:

• Confusing with Bubble Sort swapping adjacent elements
• Thinking it divides array like Merge Sort
• Assuming it uses extra data structures like heaps

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

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

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

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

Solution

1. Step 1: Identify correct swap function usage

   In C++, the standard library provides swap(a, b) to exchange values of two variables.

2. Step 2: Check syntax correctness

   swap(arr[i], arr[min_idx]); uses swap(arr[i], arr[min_idx]); which correctly swaps the two elements.

3. Final Answer:

   swap(arr[i], arr[min_idx]); -> Option A

4. Quick Check:

   Use std::swap for swapping [OK]

Hint: Use std::swap(a, b) to swap in C++ [OK]

Common Mistakes:

• Assigning one element twice causing data loss
• Using Python-style tuple swap syntax in C++
• Confusing parameter order in swap function

3. What will be the output array after running Selection Sort on arr = {64, 25, 12, 22, 11}?

medium

A. [11, 22, 12, 25, 64]

B. [64, 25, 12, 22, 11]

C. [25, 11, 12, 22, 64]

D. [11, 12, 22, 25, 64]

Solution

1. Step 1: Perform Selection Sort passes

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

2. Step 2: Final sorted array

   The array after sorting is [11, 12, 22, 25, 64].

3. Final Answer:

   [11, 12, 22, 25, 64] -> Option D

4. Quick Check:

   Selection Sort output = Sorted array ascending [OK]

Hint: Selection Sort outputs sorted ascending array [OK]

Common Mistakes:

• Not swapping minimum element correctly
• Confusing sorting order (descending vs ascending)
• Stopping before full array is sorted

4. Identify the error in the following Selection Sort code snippet:

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

medium

A. The inner loop condition should be j <= n

B. The comparison operator should be < to find minimum

C. The swap function is used incorrectly

D. The outer loop should run till i < n

Solution

1. Step 1: Analyze comparison logic

   The code uses if (arr[j] > arr[min_idx]) which finds the maximum, not minimum.

2. Step 2: Correct comparison for Selection Sort

   Selection Sort requires finding the minimum element, so the operator should be <.

3. Final Answer:

   The comparison operator should be < to find minimum -> Option B

4. Quick Check:

   Selection Sort finds minimum using < comparison [OK]

Hint: Use < to find minimum in Selection Sort [OK]

Common Mistakes:

• Using > instead of < for minimum search
• Incorrect loop boundaries causing out-of-range errors
• Misusing swap function parameters

5. Given an array arr = {5, 3, 8, 6, 2}, how many swaps will Selection Sort perform to sort it in ascending order?

hard

A. 2

B. 3

C. 4

D. 5

Solution

1. Step 1: Trace swaps during Selection Sort

   Pass 1: Minimum is 2, swap with 5 -> swap count = 1
   Array: {2, 3, 8, 6, 5}
   Pass 2: Minimum is 3, already at position -> no swap
   Pass 3: Minimum is 5, swap with 8 -> swap count = 2
   Array: {2, 3, 5, 6, 8}
   Pass 4: Minimum is 6, already at position -> no swap

2. Step 2: Count total swaps

   Total swaps performed = 2

3. Final Answer:

   2 -> Option A

4. Quick Check:

   Count swaps only when minimum differs from current [OK]

Hint: Count swaps only when minimum differs from current [OK]

Common Mistakes:

• Counting all passes as swaps
• Ignoring when minimum is already at current position
• Assuming swaps equal number of passes