2633. Convert Object to JSON String - Detailed Explanation

Problem Statement

Description:
Implement a function that converts a given object into its JSON string representation. The object can be one of the following types:

• Null: represented as null

• Boolean: represented as true or false

• Number: (integer or float) represented in numeric format

• String: must be enclosed in double quotes and properly escaped

• Array: represented as a list of JSON values, separated by commas, and enclosed in square brackets []

• Object: represented as key-value pairs (with keys always being strings), separated by commas, and enclosed in curly braces {}

Examples:

• Example 1:
  Input: obj = "Hello"
  Output: "\"Hello\""
  Explanation:
  A string should be output with double quotes around it.

• Example 2:
  Input: obj = 123
  Output: "123"
  Explanation:
  A number is represented directly as its string form.

• Example 3:
  Input: obj = [1, "two", null, true]
  Output: "[1,\"two\",null,true]"
  Explanation:
  The array elements are recursively converted to their JSON string representations and then joined with commas, enclosed in square brackets.

• Example 4:
  Input:

  {
      "name": "Alice",
      "age": 30,
      "pets": ["cat", "dog"],
      "address": null
  }

  Output:
  "{"name":"Alice","age":30,"pets":["cat","dog"],"address":null}"
  Explanation:
  Each key (always a string) and its corresponding value are recursively converted and formatted into a valid JSON object.

Constraints:

• The input can be a nested structure with any combination of the supported types.
• All keys in objects are strings.
• Proper escaping of characters in strings is required (e.g., quotes).

Hints

• Hint 1: Think recursively. Determine the type of the given object and handle it based on its type.
• Hint 2: For arrays and objects, you will need to iterate over elements or key–value pairs, convert each one using your function recursively, and then join them with the appropriate separators.
• Hint 3: Make sure to handle edge cases such as null values and proper string escaping.

Approaches

Recursive Serialization (Optimal Approach)

Concept:

• Base Cases:
  Check if the object is null, a boolean, a number, or a string. Return the proper JSON representation:
  • null → "null"
  • Boolean → "true" or "false"
  • Number → its string conversion
  • String → enclosed in double quotes with proper escaping (if needed)
• Recursive Cases:
  • Arrays:
    Iterate over each element, recursively convert each one to JSON, join the results with commas, and enclose in square brackets.
  • Objects (Dictionaries):
    Iterate over each key–value pair, recursively convert the value to JSON (the key is always a string, so ensure it’s enclosed in double quotes), join with commas, and enclose in curly braces.

Benefits:

• The recursive approach naturally handles nested structures.
• Each type is dealt with in a clear, modular way.

Alternative Approach – Using Built-In Library (Not Allowed Here)

Concept:

• In many languages, you could simply call a built-in method (e.g., JSON.stringify() in JavaScript or json.dumps() in Python).
• Note: This approach is trivial but is not acceptable if you are required to implement the conversion logic manually.

Code Implementations

Python Code (Recursive Approach)