Multiple filter parameters in Rest API - Time & Space Complexity

Time Complexity: Multiple filter parameters

O(n x k)

Understanding Time Complexity

When using multiple filter parameters in a REST API, it's important to understand how the processing time changes as the number of filters or data size grows.

We want to know how the time to handle requests grows when more filters or data are involved.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

GET /items?color=red&size=medium&brand=acme

// Server-side pseudo-code
function getFilteredItems(filters) {
  let results = allItems;
  for (const key in filters) {
    results = results.filter(item => item[key] === filters[key]);
  }
  return results;
}

This code filters a list of items by applying each filter parameter one after another.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Filtering the list of items for each filter parameter.
• How many times: Once per filter parameter, each time scanning the current list of results.

How Execution Grows With Input

As the number of items or filters increases, the filtering work grows because each filter scans the current list.

Input Size (n items)	Approx. Operations (with k filters)
10	About 10 x k
100	About 100 x k
1000	About 1000 x k

Pattern observation: The total work grows roughly in a straight line with the number of items and filters.

Final Time Complexity

Time Complexity: O(n x k)

This means the time to process grows proportionally with both the number of items and the number of filters.

Common Mistake

[X] Wrong: "Adding more filters does not affect performance much because each filter is simple."

[OK] Correct: Each filter scans the current list, so more filters mean more repeated scanning, increasing total work.

Interview Connect

Understanding how multiple filters affect performance helps you design efficient APIs and explain trade-offs clearly in interviews.

Self-Check

"What if the filters were combined into a single pass instead of multiple passes? How would the time complexity change?"

Practice

1. What does adding multiple filter parameters in a REST API URL do?
example.com/api/items?color=red&size=medium

easy

A. Returns items that match all filter conditions (color red AND size medium).

B. Returns items that match any one of the filter conditions (color red OR size medium).

C. Returns all items ignoring the filters.

D. Returns an error because multiple filters are not allowed.

Solution

1. Step 1: Understand multiple filters in URL

   Multiple filters joined by & mean the server should apply all conditions together.

2. Step 2: Interpret the example URL

   The URL ?color=red&size=medium means items must be red AND medium size.

3. Final Answer:

   Returns items that match all filter conditions (color red AND size medium). -> Option A

4. Quick Check:

   Multiple filters = AND condition [OK]

Hint: Multiple filters joined by & mean AND condition [OK]

Common Mistakes:

• Thinking filters work as OR instead of AND
• Assuming filters are ignored
• Believing multiple filters cause errors

2. Which of the following is the correct syntax to filter items by category=books and author=doe in a REST API URL?

easy

A. example.com/api/items?category=books;author=doe

B. example.com/api/items?category=books&author=doe

C. example.com/api/items?category=books|author=doe

D. example.com/api/items?category=books author=doe

Solution

1. Step 1: Identify correct separator for multiple filters

   In URLs, multiple query parameters are separated by &.

2. Step 2: Check each option

   Only example.com/api/items?category=books&author=doe uses & correctly between filters.

3. Final Answer:

   example.com/api/items?category=books&author=doe -> Option B

4. Quick Check:

   Use & to separate filters [OK]

Hint: Use & to separate multiple filters in URL [OK]

Common Mistakes:

• Using | or ; instead of &
• Leaving spaces between parameters
• Not using any separator

3. Given the REST API call:
GET /products?color=blue&size=large&in_stock=true
What kind of products will the server return?

medium

A. Products that are blue AND large AND in stock.

B. Products that are blue OR large OR in stock.

C. Products that are either blue or large, ignoring stock status.

D. All products regardless of filters.

Solution

1. Step 1: Understand multiple filters joined by &

   Filters combined with & mean all conditions must be true together.

2. Step 2: Apply to given filters

   Only products that are blue, large, and in stock will be returned.

3. Final Answer:

   Products that are blue AND large AND in stock. -> Option A

4. Quick Check:

   Multiple filters = AND condition [OK]

Hint: Multiple filters joined by & mean AND condition [OK]

Common Mistakes:

• Thinking filters combine with OR
• Ignoring some filters
• Assuming filters are optional

4. You wrote this URL to filter users by age=30 and active=true:
example.com/api/users?age=30&active=true&
But the server returns an error. What is the likely problem?

medium

A. The URL should use commas instead of &.

B. The server does not support filtering by age.

C. The filter values must be in quotes.

D. The trailing & at the end causes a syntax error.

Solution

1. Step 1: Check URL syntax for filters

   A trailing & at the end of query parameters is invalid syntax.

2. Step 2: Understand server error cause

   The server likely rejects the URL because of the extra & with no following parameter.

3. Final Answer:

   The trailing & at the end causes a syntax error. -> Option D

4. Quick Check:

   Trailing & causes error [OK]

Hint: Avoid trailing & in URL query parameters [OK]

Common Mistakes:

• Leaving trailing & at end of URL
• Using commas instead of &
• Assuming quotes are needed around values

5. You want to get all orders from the REST API where status is shipped and total is greater than 100. The API supports filtering by multiple parameters but only exact matches. How can you combine filters to get orders with status=shipped and total>100?

hard

A. Use ?status=shipped&total=100 and filter results manually.

B. Use ?status=shipped&total=gt:100 to specify greater than.

C. Use ?status=shipped&total_min=101 if the API supports range filters.

D. Use ?status=shipped&total>100 directly in URL.

Solution

1. Step 1: Understand API filter limitations

   The API only supports exact matches, so direct > operator is not allowed.

2. Step 2: Use API-supported range filter parameter

   Many APIs use parameters like total_min to filter values greater than a number.

3. Step 3: Combine filters correctly

   Using ?status=shipped&total_min=101 filters orders with status shipped and total greater than 100.

4. Final Answer:

   Use ?status=shipped&total_min=101 if the API supports range filters. -> Option C

5. Quick Check:

   Use API range params for > filters [OK]

Hint: Use API-specific range filters like total_min for > conditions [OK]

Common Mistakes:

• Trying to use > directly in URL
• Assuming all APIs support gt: syntax
• Filtering manually after fetching all data