Jobs

Interviews

Discussions

Mini Parser

#1006 Most AskedMedium

Mini Parser #1006 Most Asked

Medium

Microsoft

5 views

Topics:

StringsStacksRecursion

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].

Try coding it in LeetCode

Mini Parser

#1006 Most AskedMedium

Mini Parser #1006 Most Asked

Medium

Microsoft

5 views

Topics:

StringsStacksRecursion

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].

Try coding it in LeetCode

Solution

Clarifying Questions

When you get asked this question in a real-life environment, it will often be ambiguous (especially at FAANG). Make sure to ask these questions in that case:

What characters can appear in the input string besides digits, brackets, and commas? Do I need to handle any other special characters or whitespace?
Can the input string be empty or null?
What is the maximum nesting depth of the nested lists, and what is the maximum numerical value that can be contained within the list?
If the input string is malformed (e.g., mismatched brackets, invalid characters), should I throw an error, return a default value (like null or an empty NestedInteger), or is it guaranteed to be well-formed?
Does the input string always represent a valid NestedInteger, or are there cases where the string might not adhere to the specified format (e.g. '1,2,,3')?

Brute Force Solution

Approach

The mini parser problem involves turning a string representation of a nested list of integers into an actual nested list. The brute force approach explores all possible ways to interpret the string by recursively breaking it down and trying every possible combination of parsing the string into integers and nested lists.

Here's how the algorithm would work step-by-step:

Start reading the string from the beginning.
If you see a number, great! Convert it to an integer.
If you see an opening bracket, it means we have a nested list. Start parsing the nested list.
Keep track of where the nested list starts and ends.
Within the nested list, look for more numbers and more nested lists using the same process.
Whenever you find a number or another nested list, add it to the current list.
When you reach a closing bracket, it means the current nested list is complete. Save this list.
Continue parsing the rest of the original string after the nested list is complete, looking for more numbers and lists.
Repeat this process of finding numbers and nested lists until you've read the entire original string.
Finally, you will have a nested list of integers that represents the original string.

Code Implementation

class NestedInteger:
    def __init__(self, value=None):
        self.integer_value = value
        self.list_value = []

    def isInteger(self):
        return self.integer_value is not None

    def add(self, nestedInteger):
        self.list_value.append(nestedInteger)

    def getInteger(self):
        return self.integer_value

    def getList(self):
        return self.list_value

def parse_nested_list(string_input):
    index = 0
    def parse():
        nonlocal index
        if index >= len(string_input):
            return None

        char = string_input[index]

        if char == '[':
            index += 1
            nested_list = NestedInteger()

            # Recursively parse items in the list
            while string_input[index] != ']':
                item = parse()
                if item:
                    nested_list.add(item)
                if index < len(string_input) and string_input[index] == ',':
                    index += 1
            index += 1
            return nested_list

        elif char.isdigit() or char == '-':
            # Parse an integer
            start = index
            while index < len(string_input) and (string_input[index].isdigit() or string_input[index] == '-'):
                index += 1
            number = int(string_input[start:index])
            return NestedInteger(number)
        else:
            index += 1
            return None

    result = parse()
    return result

Big(O) Analysis

Time Complexity

O(n) – The algorithm iterates through the entire string once. Inside the loop, the primary operations are string parsing (converting substrings to integers) and recursive calls for nested lists. However, each character in the input string is processed at most once across all recursive calls. Therefore, the dominant factor is the single pass through the string, making the time complexity linear with respect to the length n of the input string.

Space Complexity

O(D) – The space complexity is primarily determined by the depth of the nested lists, where D represents the maximum nesting depth. Each opening bracket encountered leads to a recursive call, potentially creating a new stack frame to manage the parsing of the inner list. In the worst case, the input string represents a deeply nested list, resulting in a maximum recursion depth of D. Consequently, the auxiliary space required for the call stack grows linearly with the maximum nesting depth.

Optimal Solution

Approach

The core idea is to process the input string one character at a time, using a stack to keep track of nested lists. When we encounter a '[', we start a new list. When we encounter a ']', we finish the current list and add it to the list above it.

Here's how the algorithm would work step-by-step:

Start with an empty stack to hold the lists we're building.
Go through the input string, character by character.
If you see a '[', it means you're starting a new nested list. Create a new list and put it on top of the stack.
If you see a ']', it means you're finishing the list at the top of the stack. Take that list off the stack and add it as an element to the list that's now on top of the stack.
If you see a number, read the entire number and create a single number element. Then add it to the list that's currently on top of the stack.
If you see a comma, ignore it - it just separates the elements.
After processing the whole string, the final list should be the only thing left. It's either on the stack or it *is* the stack.

Code Implementation

class NestedInteger:
    def __init__(self, value=None):
        self.integer = value
        self.list = []

    def isInteger(self):
        return self.integer is not None

    def getInteger(self):
        return self.integer

    def add(self, nestedInteger):
        self.list.append(nestedInteger)

    def getList(self):
        return self.list

def deserialize(input_string):
    stack_of_nested_integers = []
    current_number = ""

    for character in input_string:
        if character == '[':
            # Start a new nested list.
            stack_of_nested_integers.append(NestedInteger())

        elif character == ']':
            # Finish a nested list and add it to the parent.
            if current_number:
                nested_integer = NestedInteger(int(current_number))
                stack_of_nested_integers[-1].add(nested_integer)
                current_number = ""

            nested_integer = stack_of_nested_integers.pop()
            if stack_of_nested_integers:
                stack_of_nested_integers[-1].add(nested_integer)
            else:
                return nested_integer

        elif character == ',':
            # Add number to list before creating the next number
            if current_number:
                nested_integer = NestedInteger(int(current_number))
                stack_of_nested_integers[-1].add(nested_integer)
                current_number = ""

        else:
            # Accumulate digits to form a number.
            current_number += character

    # Handle the case where the input is just a number.
    if current_number:
        return NestedInteger(int(current_number))

    return stack_of_nested_integers.pop()

Big(O) Analysis

Time Complexity

O(n) – The algorithm iterates through the input string of length n exactly once. Inside the loop, operations such as creating new lists, adding elements to lists, and parsing integers take constant time. The stack operations (push and pop) also take constant time. Therefore, the overall time complexity is directly proportional to the length of the input string, resulting in O(n).

Space Complexity

O(D) – The auxiliary space is primarily determined by the stack, which stores nested lists during the parsing process. The maximum depth of the nested lists in the input string 's' dictates the maximum size of the stack. In the worst-case scenario, the input consists of D nested lists, where D is the maximum nesting depth. Therefore, the space complexity is proportional to the maximum nesting depth D of the input string, resulting in O(D).

Edge Cases

Case	How to Handle
Null or empty input string	Return an empty NestedInteger or throw an exception depending on the specific problem requirements and constraints.
Input string containing only whitespace characters	Trim the input string and handle as an empty input.
Input string with mismatched brackets/parentheses	Throw an exception or return an error NestedInteger since the input is invalid.
Input string containing invalid characters (characters other than digits, '[', ']', ',', and '-')	Throw an exception as the input is malformed.
Input string with nested levels exceeding reasonable stack depth.	Limit recursion depth to avoid stack overflow; potentially use an iterative solution.
Large integer values potentially leading to overflow.	Use long data types or check for overflow conditions before constructing NestedIntegers with numerical values.
Multiple consecutive commas without any integer value in-between.	Handle as an empty NestedInteger element or throw an exception due to malformed input.
Negative numbers with leading zeros (e.g., -012)	Handle leading zeros according to the specified parsing rules or throw an exception if invalid.

Null or empty input string

How to Handle:

Return an empty NestedInteger or throw an exception depending on the specific problem requirements and constraints.

Input string containing only whitespace characters

How to Handle:

Trim the input string and handle as an empty input.

Input string with mismatched brackets/parentheses

How to Handle:

Throw an exception or return an error NestedInteger since the input is invalid.

Input string containing invalid characters (characters other than digits, '[', ']', ',', and '-')

How to Handle:

Throw an exception as the input is malformed.

Input string with nested levels exceeding reasonable stack depth.

How to Handle:

Limit recursion depth to avoid stack overflow; potentially use an iterative solution.

Large integer values potentially leading to overflow.

How to Handle:

Use long data types or check for overflow conditions before constructing NestedIntegers with numerical values.

Multiple consecutive commas without any integer value in-between.

How to Handle:

Handle as an empty NestedInteger element or throw an exception due to malformed input.

Negative numbers with leading zeros (e.g., -012)

How to Handle:

Handle leading zeros according to the specified parsing rules or throw an exception if invalid.

Solution

Clarifying Questions

When you get asked this question in a real-life environment, it will often be ambiguous (especially at FAANG). Make sure to ask these questions in that case:

What characters can appear in the input string besides digits, brackets, and commas? Do I need to handle any other special characters or whitespace?
Can the input string be empty or null?
What is the maximum nesting depth of the nested lists, and what is the maximum numerical value that can be contained within the list?
If the input string is malformed (e.g., mismatched brackets, invalid characters), should I throw an error, return a default value (like null or an empty NestedInteger), or is it guaranteed to be well-formed?
Does the input string always represent a valid NestedInteger, or are there cases where the string might not adhere to the specified format (e.g. '1,2,,3')?

Brute Force Solution

Approach

Here's how the algorithm would work step-by-step:

Start reading the string from the beginning.
If you see a number, great! Convert it to an integer.
If you see an opening bracket, it means we have a nested list. Start parsing the nested list.
Keep track of where the nested list starts and ends.
Within the nested list, look for more numbers and more nested lists using the same process.
Whenever you find a number or another nested list, add it to the current list.
When you reach a closing bracket, it means the current nested list is complete. Save this list.
Continue parsing the rest of the original string after the nested list is complete, looking for more numbers and lists.
Repeat this process of finding numbers and nested lists until you've read the entire original string.
Finally, you will have a nested list of integers that represents the original string.

Code Implementation

class NestedInteger:
    def __init__(self, value=None):
        self.integer_value = value
        self.list_value = []

    def isInteger(self):
        return self.integer_value is not None

    def add(self, nestedInteger):
        self.list_value.append(nestedInteger)

    def getInteger(self):
        return self.integer_value

    def getList(self):
        return self.list_value

def parse_nested_list(string_input):
    index = 0
    def parse():
        nonlocal index
        if index >= len(string_input):
            return None

        char = string_input[index]

        if char == '[':
            index += 1
            nested_list = NestedInteger()

            # Recursively parse items in the list
            while string_input[index] != ']':
                item = parse()
                if item:
                    nested_list.add(item)
                if index < len(string_input) and string_input[index] == ',':
                    index += 1
            index += 1
            return nested_list

        elif char.isdigit() or char == '-':
            # Parse an integer
            start = index
            while index < len(string_input) and (string_input[index].isdigit() or string_input[index] == '-'):
                index += 1
            number = int(string_input[start:index])
            return NestedInteger(number)
        else:
            index += 1
            return None

    result = parse()
    return result

Big(O) Analysis

Time Complexity

Space Complexity

Optimal Solution

Approach

Here's how the algorithm would work step-by-step:

Start with an empty stack to hold the lists we're building.
Go through the input string, character by character.
If you see a '[', it means you're starting a new nested list. Create a new list and put it on top of the stack.
If you see a ']', it means you're finishing the list at the top of the stack. Take that list off the stack and add it as an element to the list that's now on top of the stack.
If you see a number, read the entire number and create a single number element. Then add it to the list that's currently on top of the stack.
If you see a comma, ignore it - it just separates the elements.
After processing the whole string, the final list should be the only thing left. It's either on the stack or it *is* the stack.

Code Implementation

class NestedInteger:
    def __init__(self, value=None):
        self.integer = value
        self.list = []

    def isInteger(self):
        return self.integer is not None

    def getInteger(self):
        return self.integer

    def add(self, nestedInteger):
        self.list.append(nestedInteger)

    def getList(self):
        return self.list

def deserialize(input_string):
    stack_of_nested_integers = []
    current_number = ""

    for character in input_string:
        if character == '[':
            # Start a new nested list.
            stack_of_nested_integers.append(NestedInteger())

        elif character == ']':
            # Finish a nested list and add it to the parent.
            if current_number:
                nested_integer = NestedInteger(int(current_number))
                stack_of_nested_integers[-1].add(nested_integer)
                current_number = ""

            nested_integer = stack_of_nested_integers.pop()
            if stack_of_nested_integers:
                stack_of_nested_integers[-1].add(nested_integer)
            else:
                return nested_integer

        elif character == ',':
            # Add number to list before creating the next number
            if current_number:
                nested_integer = NestedInteger(int(current_number))
                stack_of_nested_integers[-1].add(nested_integer)
                current_number = ""

        else:
            # Accumulate digits to form a number.
            current_number += character

    # Handle the case where the input is just a number.
    if current_number:
        return NestedInteger(int(current_number))

    return stack_of_nested_integers.pop()

Big(O) Analysis

Time Complexity

Space Complexity

Edge Cases

Case	How to Handle
Null or empty input string	Return an empty NestedInteger or throw an exception depending on the specific problem requirements and constraints.
Input string containing only whitespace characters	Trim the input string and handle as an empty input.
Input string with mismatched brackets/parentheses	Throw an exception or return an error NestedInteger since the input is invalid.
Input string containing invalid characters (characters other than digits, '[', ']', ',', and '-')	Throw an exception as the input is malformed.
Input string with nested levels exceeding reasonable stack depth.	Limit recursion depth to avoid stack overflow; potentially use an iterative solution.
Large integer values potentially leading to overflow.	Use long data types or check for overflow conditions before constructing NestedIntegers with numerical values.
Multiple consecutive commas without any integer value in-between.	Handle as an empty NestedInteger element or throw an exception due to malformed input.
Negative numbers with leading zeros (e.g., -012)	Handle leading zeros according to the specified parsing rules or throw an exception if invalid.

Null or empty input string

How to Handle:

Return an empty NestedInteger or throw an exception depending on the specific problem requirements and constraints.

Input string containing only whitespace characters

How to Handle:

Trim the input string and handle as an empty input.

Input string with mismatched brackets/parentheses

How to Handle:

Throw an exception or return an error NestedInteger since the input is invalid.

Input string containing invalid characters (characters other than digits, '[', ']', ',', and '-')

How to Handle:

Throw an exception as the input is malformed.

Input string with nested levels exceeding reasonable stack depth.

How to Handle:

Limit recursion depth to avoid stack overflow; potentially use an iterative solution.

Large integer values potentially leading to overflow.

How to Handle:

Use long data types or check for overflow conditions before constructing NestedIntegers with numerical values.

Multiple consecutive commas without any integer value in-between.

How to Handle:

Handle as an empty NestedInteger element or throw an exception due to malformed input.

Negative numbers with leading zeros (e.g., -012)

How to Handle:

Handle leading zeros according to the specified parsing rules or throw an exception if invalid.

0/1114 Microsoft questions completed

0/1114 completed