Is Mini Parser easy or hard?

Mini Parser is usually rated Medium difficulty. The challenge comes from correctly handling nested structures, multi-digit numbers, and negative values while building the nested object representation in a single pass.

How to solve Mini Parser in O(n)?

Parse the string from left to right and construct NestedInteger objects while tracking nesting levels. Using a stack, push a new list when encountering '[' and pop when encountering ']'. Numbers are parsed and appended directly. Because each character is processed once, the algorithm runs in O(n) time.

What is the best approach for Mini Parser?

The stack-based parsing approach is generally considered the best solution. It processes the string sequentially while maintaining a stack to track nested lists. Each character is handled once, giving O(n) time complexity and O(n) space complexity for deeply nested structures.

What data structure is used in Mini Parser?

A stack is the primary data structure used in the iterative solution. It tracks parent lists while parsing nested brackets. The recursive approach instead relies on the call stack to manage nested levels during depth-first parsing.

What is the time complexity of Mini Parser?

The optimal time complexity is O(n), where n is the length of the input string. Each character is processed exactly once during parsing, whether using the stack-based iterative method or recursive deserialization.

Mini Parser Python or Java solution approach

Both Python and Java solutions follow the same logic: parse characters, detect integers, and manage nested lists using a stack or recursion. Python implementations often use simple loops and lists, while Java solutions build NestedInteger objects and maintain a Stack for hierarchy tracking.

Is Mini Parser asked at Google, Amazon, or Meta?

Serialization and deserialization problems like Mini Parser appear in interviews at large tech companies including Amazon, Google, and Meta. The problem tests parsing logic, stack usage, and handling nested structures—skills commonly evaluated in system and data structure interviews.

Description Solution Video 12:04

385. Mini Parser

Medium44.0% acceptance4 companies

Given a string s represents the serialization of a nested list, implement a parser to deserialize it and return the deserialized NestedInteger.

Each element is either an integer or a list whose elements may also be integers or other lists.

Example 1:

Input: s = "324"
Output: 324
Explanation: You should return a NestedInteger object which contains a single integer 324.

Example 2:

Input: s = "[123,[456,[789]]]"
Output: [123,[456,[789]]]
Explanation: Return a NestedInteger object containing a nested list with 2 elements:
1. An integer containing value 123.
2. A nested list containing two elements:
    i.  An integer containing value 456.
    ii. A nested list with one element:
         a. An integer containing value 789

Constraints:

1 <= s.length <= 5 * 10⁴
s consists of digits, square brackets "[]", negative sign '-', and commas ','.
s is the serialization of valid NestedInteger.
All the values in the input are in the range [-10⁶, 10⁶].

Asked at 4 companies

Airbnb Amazon Meta Bloomberg

Topics

12:04

Still stuck?Read 4 approaches, or watch a walkthrough.

Open solution

Similar problems

Flatten Nested List IteratorMedium Ternary Expression ParserMedium Remove CommentsMedium

LanguageLoading editor…

1# """
2# This is the interface that allows for creating nested lists.
3# You should not implement it, or speculate about its implementation
4# """
5#class NestedInteger:
6#    def __init__(self, value=None):
7#        """
8#        If value is not specified, initializes an empty list.
9#        Otherwise initializes a single integer equal to value.
10#        """
11#
12#    def isInteger(self):
13#        """
14#        @return True if this NestedInteger holds a single integer, rather than a nested list.
15#        :rtype bool
16#        """
17#
18#    def add(self, elem):
19#        """
20#        Set this NestedInteger to hold a nested list and adds a nested integer elem to it.
21#        :rtype void
22#        """
23#
24#    def setInteger(self, value):
25#        """
26#        Set this NestedInteger to hold a single integer equal to value.
27#        :rtype void
28#        """
29#
30#    def getInteger(self):
31#        """
32#        @return the single integer that this NestedInteger holds, if it holds a single integer
33#        Return None if this NestedInteger holds a nested list
34#        :rtype int
35#        """
36#
37#    def getList(self):
38#        """
39#        @return the nested list that this NestedInteger holds, if it holds a nested list
40#        Return None if this NestedInteger holds a single integer
41#        :rtype List[NestedInteger]
42#        """
43 
44class Solution:
45    def deserialize(self, s: str) -> NestedInteger:
46        

Starter codePython 3Spaces: 4

Examples

Case 1Case 2

Input

"324"

Input

"[123,[456,[789]]]"

Your code is saved on this device.Solution