DELETE for removing resources in Rest API - Time & Space Complexity

Time Complexity: DELETE for removing resources

O(n)

Understanding Time Complexity

When we use DELETE requests in REST APIs, we want to know how long it takes to remove data as the amount of data grows.

We ask: How does the time to delete change when there are more resources?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

DELETE /items/{id}

// Server receives DELETE request
// Finds item by id
// Removes item from database
// Sends response confirming deletion

This code deletes one item identified by its unique id from the database.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Searching for the item by its id in the database.
• How many times: This happens once per DELETE request.

How Execution Grows With Input

Explain the growth pattern intuitively.

Input Size (n)	Approx. Operations
10	About 10 steps to find the item
100	About 100 steps to find the item
1000	About 1000 steps to find the item

Pattern observation: The time to find and delete grows roughly in direct proportion to the number of items.

Final Time Complexity

Time Complexity: O(n)

This means the time to delete an item grows linearly with the number of items in the database.

Common Mistake

[X] Wrong: "Deleting one item always takes the same time, no matter how many items exist."

[OK] Correct: If the database searches items by scanning all entries, more items mean more time to find the one to delete.

Interview Connect

Understanding how DELETE requests scale helps you explain backend performance clearly and shows you know how data size affects response time.

Self-Check

"What if the database used an index to find items by id? How would the time complexity change?"

Practice

1. What is the main purpose of the HTTP DELETE method in REST APIs?

easy

A. To remove a resource identified by a URL

B. To create a new resource on the server

C. To update an existing resource

D. To retrieve data from the server

Solution

1. Step 1: Understand HTTP methods

   HTTP methods define actions on resources. DELETE is specifically for removal.

2. Step 2: Identify DELETE's role

   DELETE removes the resource at the given URL, unlike POST (create), PUT/PATCH (update), or GET (retrieve).

3. Final Answer:

   To remove a resource identified by a URL -> Option A

4. Quick Check:

   DELETE = remove resource [OK]

Hint: DELETE always removes resource at the URL, no body needed [OK]

Common Mistakes:

• Confusing DELETE with GET or POST
• Thinking DELETE requires a request body
• Assuming DELETE creates or updates data

2. Which of the following is the correct syntax to send a DELETE request to remove a user with ID 123 using curl?

easy

A. curl -X GET https://api.example.com/users/123

B. curl -X PUT https://api.example.com/users/123

C. curl -X POST https://api.example.com/users/123

D. curl -X DELETE https://api.example.com/users/123

Solution

1. Step 1: Identify HTTP method for deletion

   DELETE method is used to remove resources, so -X DELETE is correct.

2. Step 2: Check URL and method usage

   The URL targets user 123, and curl uses -X to specify method. So, curl -X DELETE URL is correct.

3. Final Answer:

   curl -X DELETE https://api.example.com/users/123 -> Option D

4. Quick Check:

   curl DELETE syntax = curl -X DELETE URL [OK]

Hint: Use curl -X DELETE followed by resource URL [OK]

Common Mistakes:

• Using GET or POST instead of DELETE
• Omitting the -X flag for method
• Using PUT which is for updates

3. Given this Python code using requests library:

import requests
response = requests.delete('https://api.example.com/items/45')
print(response.status_code)

What will be printed if the item was successfully deleted?

medium

A. 201

B. 404

C. 200

D. 500

Solution

1. Step 1: Understand HTTP status codes for DELETE

   Successful DELETE usually returns 200 (OK) or 204 (No Content). 200 means success with response body.

2. Step 2: Check options for success code

   Among options, 200 indicates success. 404 means not found, 500 server error, 201 created (not for DELETE).

3. Final Answer:

   200 -> Option C

4. Quick Check:

   DELETE success = 200 OK [OK]

Hint: Successful DELETE usually returns 200 or 204 status code [OK]

Common Mistakes:

• Confusing 201 (created) with success for DELETE
• Assuming 404 means success
• Ignoring status code meanings

4. Consider this JavaScript fetch code to delete a post:

fetch('https://api.example.com/posts/10', {
  method: 'DELETE',
  body: JSON.stringify({ id: 10 })
})
.then(res => res.status)
.then(console.log)

What is the main issue with this code?

medium

A. The URL is incorrect

B. DELETE requests should not have a body

C. The method should be GET

D. Missing headers for JSON content

Solution

1. Step 1: Understand DELETE request body rules

   DELETE usually does not require a request body; many servers ignore or reject it.

2. Step 2: Identify the problem in code

   The code sends a JSON body with DELETE, which is often unnecessary and may cause errors.

3. Final Answer:

   DELETE requests should not have a body -> Option B

4. Quick Check:

   DELETE usually no body [OK]

Hint: Avoid sending body with DELETE requests [OK]

Common Mistakes:

• Adding unnecessary body to DELETE
• Confusing method with GET or POST
• Forgetting to check server docs for DELETE body support

5. You want to delete multiple resources in one request using REST API. Which approach is best practice?

hard

A. Send multiple DELETE requests, one per resource URL

B. Send a single DELETE request with a JSON array body listing IDs

C. Use POST method with action=delete and list of IDs in body

D. Use GET method with query parameters to delete resources

Solution

1. Step 1: Understand REST principles for DELETE

   DELETE targets a single resource URL. Bulk delete is not standardized and often unsupported.

2. Step 2: Evaluate options for bulk deletion

   Sending multiple DELETE requests (one per resource) is standard and reliable. Other methods misuse HTTP verbs or semantics.

3. Final Answer:

   Send multiple DELETE requests, one per resource URL -> Option A

4. Quick Check:

   One DELETE per resource URL [OK]

Hint: Delete resources one by one with separate DELETE requests [OK]

Common Mistakes:

• Trying to send bulk delete in one DELETE with body
• Using POST or GET to delete resources
• Assuming server supports bulk delete by default