JSON as standard format in Rest API - Time & Space Complexity

Time Complexity: JSON as standard format

O(n)

Understanding Time Complexity

When working with REST APIs, JSON is the common way to send and receive data. Understanding how processing JSON scales helps us build faster apps.

We want to know how the time to handle JSON changes as the data size grows.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

// Example: Parsing JSON data from an API response
const jsonData = '{"users": [{"id": 1}, {"id": 2}, {"id": 3}]}';
const data = JSON.parse(jsonData);
for (const user of data.users) {
  console.log(user.id);
}
    

This code parses a JSON string and loops through the users to print their IDs.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Looping through the array of users after parsing JSON.
• How many times: Once for each user in the array.

How Execution Grows With Input

As the number of users grows, the time to parse and loop grows too.

Input Size (n)	Approx. Operations
10	About 10 loops plus parsing
100	About 100 loops plus parsing
1000	About 1000 loops plus parsing

Pattern observation: The time grows roughly in direct proportion to the number of users.

Final Time Complexity

Time Complexity: O(n)

This means the time to process the JSON grows linearly with the number of items inside it.

Common Mistake

[X] Wrong: "Parsing JSON is instant and does not depend on data size."

[OK] Correct: Parsing reads every character, so bigger JSON takes more time to process.

Interview Connect

Knowing how JSON parsing and data traversal scale helps you explain API performance clearly and confidently.

Self-Check

"What if we used nested JSON objects instead of a flat array? How would the time complexity change?"

Practice

1. What is the main reason REST APIs use JSON as their standard format?

easy

A. Because JSON is easy to read and write for both humans and machines

B. Because JSON requires special software to understand

C. Because JSON is a binary format

D. Because JSON only supports numbers

Solution

1. Step 1: Understand JSON format

   JSON is a text-based format that uses simple syntax with objects and arrays.

2. Step 2: Identify why REST APIs prefer JSON

   REST APIs use JSON because it is easy for humans to read and easy for machines to parse.

3. Final Answer:

   Because JSON is easy to read and write for both humans and machines -> Option A

4. Quick Check:

   JSON is text-based and readable [OK]

Hint: JSON is popular because it's simple and readable [OK]

Common Mistakes:

• Thinking JSON is binary
• Believing JSON needs special software
• Assuming JSON only supports numbers

2. Which of the following is the correct JSON syntax for an object with a key "name" and value "Alice"?

easy

A. {"name" = "Alice"}

B. {name: "Alice"}

C. ["name": "Alice"]

D. {"name": "Alice"}

Solution

1. Step 1: Recall JSON object syntax

   JSON objects use curly braces with keys and values as strings, keys must be in double quotes.

2. Step 2: Check each option

   {"name": "Alice"} uses double quotes correctly around key and value, with colon separator.

3. Final Answer:

   {"name": "Alice"} -> Option D

4. Quick Check:

   Keys and strings in double quotes [OK]

Hint: Keys and string values must be in double quotes [OK]

Common Mistakes:

• Omitting quotes around keys
• Using square brackets for objects
• Using equals sign instead of colon

3. Given this JSON response from a REST API:

{"status": "success", "data": [10, 20, 30]}

What is the value of the key "data"?

medium

A. "success"

B. [10, 20, 30]

C. 10

D. {"status": "success"}

Solution

1. Step 1: Identify the key "data" in JSON

   The key "data" holds an array with values 10, 20, and 30.

2. Step 2: Match the value to the options

   [10, 20, 30] correctly shows the array [10, 20, 30].

3. Final Answer:

   [10, 20, 30] -> Option B

4. Quick Check:

   Key "data" = array [10, 20, 30] [OK]

Hint: Look for the key and read its value exactly as shown [OK]

Common Mistakes:

• Confusing key "status" value with "data"
• Picking a single number instead of the array
• Choosing the whole JSON object as value

4. You receive this JSON string from an API:

{"user": "Bob", "age": 25,}

What is wrong with this JSON?

medium

A. Trailing comma after the last item is invalid

B. Keys must be numbers, not strings

C. Values cannot be numbers

D. Missing square brackets around the object

Solution

1. Step 1: Check JSON syntax rules

   JSON objects cannot have a comma after the last key-value pair.

2. Step 2: Identify the error in the string

   The comma after "age": 25 is invalid and causes a syntax error.

3. Final Answer:

   Trailing comma after the last item is invalid -> Option A

4. Quick Check:

   No trailing commas allowed in JSON objects [OK]

Hint: No commas after last item in JSON objects [OK]

Common Mistakes:

• Thinking keys must be numbers
• Believing numbers are invalid values
• Adding brackets incorrectly

5. You want to send a JSON payload to a REST API with user info: name "Eve", age 28, and hobbies as an array of "reading" and "swimming". Which JSON is correct?

hard

A. {"name": "Eve", "age": 28, "hobbies": "reading, swimming"}

B. {"name": Eve, "age": "28", "hobbies": ("reading", "swimming")}

C. {"name": "Eve", "age": 28, "hobbies": ["reading", "swimming"]}

D. {"name": "Eve", "age": 28, "hobbies": {"reading", "swimming"}}

Solution

1. Step 1: Check correct JSON types for each field

   Name is a string, age is a number, hobbies is an array of strings.

2. Step 2: Validate each option's syntax

   {"name": "Eve", "age": 28, "hobbies": ["reading", "swimming"]} correctly uses double quotes for strings, numbers without quotes, and square brackets for array.

3. Final Answer:

   {"name": "Eve", "age": 28, "hobbies": ["reading", "swimming"]} -> Option C

4. Quick Check:

   Strings in quotes, numbers plain, arrays in brackets [OK]

Hint: Use quotes for strings, brackets for arrays, no quotes for numbers [OK]

Common Mistakes:

• Using parentheses instead of brackets for arrays
• Not quoting string values
• Putting numbers in quotes unnecessarily