Practice/Meta/Leetcode 2759. Convert JSON String to Object

Leetcode 2759. Convert JSON String to Object

CodingOptional

Problem

Create a parser that takes a valid JSON-formatted string as input and converts it into the appropriate native data structure. Your parser must handle all standard JSON types: objects (key-value mappings), arrays, strings with escape sequences, numbers (integers and decimals), booleans, and null values.

The parser should process the string character by character, building the nested structure while respecting JSON syntax rules. It must correctly handle whitespace, nested structures of arbitrary depth, and string escape sequences like \n, \t, \", and \\.

Requirements

1. Parse JSON objects enclosed in curly braces with key-value pairs
2. Parse JSON arrays enclosed in square brackets
3. Handle string values with proper escape sequence interpretation
4. Parse numbers (positive, negative, integers, and floating-point)
5. Recognize boolean literals true and false
6. Recognize null as a valid value
7. Skip whitespace characters (spaces, tabs, newlines) appropriately
8. Support arbitrary nesting of objects and arrays

Constraints

• Input string length: 1 ≤ n ≤ 10,000 characters
• You may assume the input is always valid JSON (no syntax error handling required)
• Maximum nesting depth: 100 levels
• Time complexity target: O(n) where n is the string length
• Space complexity: O(n) for the output structure and call stack

Examples

Example 1:

Input: '{"name": "Charlie", "age": 25}' Output: \{"name": "Charlie", "age": 25\} Explanation: A simple object with two properties is parsed into a dictionary/object with string and number values.

Example 2:

Input: '[1, 2, 3, 4, 5]' Output: [1, 2, 3, 4, 5] Explanation: An array of integers is parsed into a list/array.

Example 3:

Input: '{"items": [true, false, null], "count": 3}' Output: \{"items": [true, false, null], "count": 3\} Explanation: An object containing an array of boolean and null values, plus a number property.

Example 4:

Input: '{"text": "Hello\\nWorld"}' Output: \{"text": "Hello\nWorld"\} Explanation: The escape sequence \\n is interpreted as an actual newline character.