Selection Sort Algorithm in DSA Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main idea behind the Selection Sort algorithm?

Selection Sort repeatedly finds the smallest element from the unsorted part and moves it to the beginning, sorting the list step by step.

beginner

How many passes does Selection Sort make over the array?

Selection Sort makes n-1 passes over an array of n elements, because after placing n-1 elements, the last one is already sorted.

intermediate

What is the time complexity of Selection Sort in the average and worst cases?

The time complexity is O(n²) because it uses two nested loops: one to select the position and one to find the minimum element.

beginner

Does Selection Sort require extra space for sorting?

No, Selection Sort sorts the array in place and requires only a constant amount of extra space (O(1)).

beginner

Show the first step of Selection Sort on the array [29, 10, 14, 37, 13].

Find the smallest element (10) and swap it with the first element (29). The array becomes [10, 29, 14, 37, 13].

What does Selection Sort do in each pass?

A Finds the smallest element and swaps it to the front

B Swaps adjacent elements if they are in wrong order

C Divides the array into halves and sorts each

D Builds a heap to sort elements

Selection Sort finds the smallest element in the unsorted part and swaps it to the front in each pass.

What is the best case time complexity of Selection Sort?

A O(n log n)

B O(n²)

C O(n)

D O(log n)

Selection Sort always takes O(n²) time because it scans the entire unsorted part to find the minimum element.

How much extra memory does Selection Sort need?

A O(n²)

B O(log n)

C O(n)

D O(1)

Selection Sort sorts the array in place and needs only constant extra space.

Which of these is true about Selection Sort?

A It is a stable sorting algorithm

B It is faster than Quick Sort on large arrays

C It is an unstable sorting algorithm

D It uses divide and conquer

Selection Sort is unstable because swapping can change the order of equal elements.

After the first pass of Selection Sort on [5, 3, 8, 4], what is the array?

A [3, 5, 8, 4]

B [5, 3, 8, 4]

C [3, 4, 5, 8]

D [4, 3, 8, 5]

The smallest element 3 is swapped with the first element 5, resulting in [3, 5, 8, 4].

Explain how Selection Sort works step by step on a small array.

Think about how you pick the smallest item and place it at the start repeatedly.

Compare Selection Sort with Bubble Sort in terms of time complexity and stability.

Consider how each algorithm moves elements and whether equal elements keep their order.