Insertion Sort Algorithm in DSA C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the basic idea behind the Insertion Sort algorithm?

Insertion Sort builds the final sorted list one item at a time by taking each element and inserting it into its correct position among the previously sorted elements.

beginner

What is the time complexity of Insertion Sort in the worst case?

The worst-case time complexity of Insertion Sort is O(n²), where n is the number of elements to sort. This happens when the list is sorted in reverse order.

intermediate

How does Insertion Sort behave with nearly sorted data?

Insertion Sort performs very efficiently on nearly sorted data, with a time complexity close to O(n), because fewer shifts are needed to insert elements in their correct positions.

beginner

Show the step-by-step insertion of the element 5 into the sorted list [1, 3, 7, 9] using Insertion Sort.

Step 1: Compare 5 with 9, shift 9 right.<br>Step 2: Compare 5 with 7, shift 7 right.<br>Step 3: Compare 5 with 3, stop shifting.<br>Step 4: Insert 5 after 3.<br>Resulting list: [1, 3, 5, 7, 9]

beginner

What is the space complexity of Insertion Sort?

Insertion Sort has a space complexity of O(1) because it sorts the list in place without needing extra space proportional to the input size.

What does Insertion Sort do at each step?

A Selects the smallest element and swaps it with the first

B Inserts the current element into the correct position in the sorted part

C Divides the list into two halves

D Swaps the current element with the last element

Insertion Sort takes the current element and inserts it into the correct position among the already sorted elements.

What is the best-case time complexity of Insertion Sort?

A O(n)

B O(n²)

C O(n log n)

D O(log n)

When the list is already sorted, Insertion Sort only compares each element once, resulting in O(n) time.

Which of these is true about Insertion Sort?

A It divides the list into sublists

B It requires extra memory proportional to the input size

C It always performs better than Quick Sort

D It is stable and sorts in place

Insertion Sort is stable (preserves order of equal elements) and sorts the list in place without extra memory.

In Insertion Sort, what happens when the current element is smaller than elements in the sorted part?

A Those elements are shifted right to make space

B The current element is discarded

C The list is reversed

D The current element is swapped with the first element

Elements larger than the current element are shifted right to insert the current element in the correct position.

Which scenario causes the worst-case performance for Insertion Sort?

A List contains all equal elements

B List is already sorted

C List is sorted in reverse order

D List is empty

When the list is sorted in reverse order, every element must be compared and shifted, causing O(n²) time.

Explain how Insertion Sort works step-by-step on a small list.

Think about sorting playing cards in your hand.

Describe the time and space complexity of Insertion Sort and when it performs best.

Consider how many comparisons and shifts happen depending on input order.