Introduction

In this blog post, we will explore how to solve the LeetCode problem "385" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

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].

Explanation

Here's the breakdown of the solution:

• Recursive Descent Parsing: The problem naturally lends itself to recursive descent parsing. We process the string character by character. If we encounter a '[', we recursively parse the nested list. If we encounter a number, we parse it as an integer.
• Handling nested structures: Utilize the call stack to keep track of the current nested level and manage element additions to the appropriate NestedInteger object.

• String processing optimization: Iterate through the string efficiently using an index to avoid unnecessary string slicing, which improves performance.

• Time & Space Complexity: Time: O(N), where N is the length of the string. Space: O(D), where D is the maximum depth of the nested list due to the recursive call stack.

Code

    # """
# This is the interface that allows for creating nested lists.
# You should not implement it, or speculate about its implementation
# """
class NestedInteger:
    def __init__(self, value=None):
        """
        If value is not specified, initializes an empty list.
        Otherwise initializes a single integer equal to value.
        """
        if value is None:
            self.integer = None
            self.list = []
        else:
            self.integer = value
            self.list = None

    def isInteger(self):
        """
        @return True if this NestedInteger holds a single integer, rather than a nested list.
        :rtype bool
        """
        return self.list is None

    def add(self, elem):
        """
        Set this NestedInteger to hold a nested list and adds a nested integer elem to it.
        :rtype void
        """
        if self.integer is not None:
            self.list = []
            self.list.append(NestedInteger(self.integer)) #copy current int to list
            self.integer = None
        self.list.append(elem)

    def setInteger(self, value):
        """
        Set this NestedInteger to hold a single integer equal to value.
        :rtype void
        """
        self.integer = value
        self.list = None

    def getInteger(self):
        """
        @return the single integer that this NestedInteger holds, if it holds a single integer
        Return None if this NestedInteger holds a nested list
        :rtype int
        """
        return self.integer

    def getList(self):
        """
        @return the nested list that this NestedInteger holds, if it holds a nested list
        Return None if this NestedInteger holds a single integer
        :rtype List[NestedInteger]
        """
        return self.list

class Solution:
    def deserialize(self, s: str) -> NestedInteger:
        def parse(s, index):
            if s[index].isdigit() or s[index] == '-':
                negative = False
                if s[index] == '-':
                    negative = True
                    index += 1
                num = 0
                while index < len(s) and s[index].isdigit():
                    num = num * 10 + int(s[index])
                    index += 1
                if negative:
                    num = -num
                return NestedInteger(num), index
            else:
                ni = NestedInteger()
                index += 1  # Skip '['
                while index < len(s) and s[index] != ']':
                    nested_integer, index = parse(s, index)
                    ni.add(nested_integer)
                    if index < len(s) and s[index] == ',':
                        index += 1
                index += 1  # Skip ']'
                return ni, index

        return parse(s, 0)[0]