Sort direction (asc, desc) in Rest API - Time & Space Complexity

Time Complexity: Sort direction (asc, desc)

O(n log n)

Understanding Time Complexity

When sorting data in ascending or descending order, it is important to understand how the time taken grows as the data size increases.

We want to know how the sorting operation's cost changes when we have more items to sort.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

GET /items?sort=asc

// Server fetches all items
// Then sorts items by price ascending or descending
const sortedItems = items.sort((a, b) => {
  if (sortDirection === 'asc') return a.price - b.price;
  else return b.price - a.price;
});
return sortedItems;
    

This code sorts a list of items by their price in either ascending or descending order based on the request.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The sorting algorithm compares pairs of items multiple times.
• How many times: The number of comparisons grows as the list size increases, usually more than once per item.

How Execution Grows With Input

As the number of items grows, the sorting takes more time because it must compare many pairs.

Input Size (n)	Approx. Operations
10	About 30 comparisons
100	About 700 comparisons
1000	About 10,000 comparisons

Pattern observation: The number of operations grows faster than the number of items, roughly as n log n.

Final Time Complexity

Time Complexity: O(n log n)

This means that as the list grows, the time to sort grows a bit faster than the list size but much slower than checking every pair.

Common Mistake

[X] Wrong: "Sorting ascending is faster than sorting descending because it feels simpler."

[OK] Correct: Both ascending and descending sorting use the same process and take about the same time regardless of direction.

Interview Connect

Understanding how sorting time grows helps you explain performance in real apps where users want data sorted quickly.

Self-Check

"What if the items were already sorted? How would that affect the time complexity of sorting in ascending or descending order?"

Practice

1.

What does the direction=asc parameter do in a REST API request?

easy

A. Sorts the data in ascending order, from smallest to largest.

B. Sorts the data in descending order, from largest to smallest.

C. Filters the data to show only ascending values.

D. Deletes all data except the first item.

Solution

1. Step 1: Understand the meaning of 'asc'

   'asc' stands for ascending, which means sorting from smallest to largest.

2. Step 2: Apply to REST API sorting

   When used as a direction parameter, it orders the data from smallest to largest values.

3. Final Answer:

   Sorts the data in ascending order, from smallest to largest. -> Option A

4. Quick Check:

   direction=asc means ascending order [OK]

Hint: Asc means smallest to largest order in sorting [OK]

Common Mistakes:

• Confusing 'asc' with descending order
• Thinking 'asc' filters data instead of sorting
• Assuming 'asc' deletes data

2.

Which of the following is the correct way to specify descending sort direction in a REST API URL query?

https://api.example.com/items?sort=price&_____

easy

A. direction=asc

B. order=asc

C. sort=desc

D. direction=desc

Solution

1. Step 1: Identify the parameter for sort direction

   The common parameter to specify sort direction is 'direction'.

2. Step 2: Choose the correct value for descending order

   Descending order is indicated by 'desc'. So the correct query is 'direction=desc'.

3. Final Answer:

   direction=desc -> Option D

4. Quick Check:

   Descending sort uses direction=desc [OK]

Hint: Use direction=desc for descending sort in query [OK]

Common Mistakes:

• Using 'sort=desc' instead of 'direction=desc'
• Mixing 'asc' and 'desc' values
• Using 'order=asc' which is not standard here

3.

Given this REST API response sorted by rating in descending order, what is the first item's rating?

GET https://api.example.com/movies?sort=rating&direction=desc

Response:
[
  {"title": "Movie A", "rating": 9.5},
  {"title": "Movie B", "rating": 8.7},
  {"title": "Movie C", "rating": 7.9}
]

medium

A. 7.9

B. 8.7

C. 9.5

D. Cannot determine

Solution

1. Step 1: Understand descending order sorting

   Descending order means highest values come first.

2. Step 2: Check the first item in the response

   The first item has rating 9.5, which is the highest rating.

3. Final Answer:

   9.5 -> Option C

4. Quick Check:

   Descending sort puts 9.5 first [OK]

Hint: Descending means highest value is first in list [OK]

Common Mistakes:

• Picking the last item's rating instead of first
• Confusing ascending with descending order
• Choosing 'Cannot determine' without checking response

4.

Identify the error in this REST API request URL that tries to sort users by age in descending order:

https://api.example.com/users?sort=age&direction=descending

medium

A. The parameter 'direction' should be 'desc' not 'descending'.

B. The 'sort' parameter should be 'desc' instead of 'age'.

C. The URL is missing the 'order' parameter.

D. The '&' symbol should be replaced with '?' in the URL.

Solution

1. Step 1: Check the 'direction' parameter value

   The correct values for direction are 'asc' or 'desc', not 'descending'.

2. Step 2: Confirm the 'sort' parameter is correct

   'sort=age' is correct to specify sorting by age.

3. Final Answer:

   The parameter 'direction' should be 'desc' not 'descending'. -> Option A

4. Quick Check:

   Use 'desc' for descending direction [OK]

Hint: Use 'desc' not 'descending' for direction [OK]

Common Mistakes:

• Using full word 'descending' instead of 'desc'
• Changing 'sort' parameter incorrectly
• Misplacing '&' and '?' in URL

5.

You want to get a list of products sorted by price ascending, but only those with price greater than 100. Which query parameters correctly combine sorting and filtering?

hard

A. sort=price&direction=desc&filter=price>100

B. filter=price>100&sort=price&direction=asc

C. sort=price&direction=asc&filter=price=100

D. direction=asc&filter=price>100

Solution

1. Step 1: Identify sorting parameters

   Sorting by price ascending requires 'sort=price' and 'direction=asc'.

2. Step 2: Add filtering for price greater than 100

   Filtering is done with 'filter=price>100'. The order of parameters does not affect functionality but including all is best practice.

3. Final Answer:

   filter=price>100&sort=price&direction=asc -> Option B

4. Quick Check:

   Filter then sort ascending with correct parameters [OK]

Hint: Combine filter and sort with correct parameters [OK]

Common Mistakes:

• Using descending direction instead of ascending
• Omitting filter parameter
• Incorrect parameter order causing confusion