Split Message Based on Limit

Hard

Capital One

1 view

Topics:

Strings

You are given a string, message, and a positive integer, limit.

You must split message into one or more parts based on limit. Each resulting part should have the suffix "<a/b>", where "b" is to be replaced with the total number of parts and "a" is to be replaced with the index of the part, starting from 1 and going up to b. Additionally, the length of each resulting part (including its suffix) should be equal to limit, except for the last part whose length can be at most limit.

The resulting parts should be formed such that when their suffixes are removed and they are all concatenated in order, they should be equal to message. Also, the result should contain as few parts as possible.

Return the parts message would be split into as an array of strings. If it is impossible to split message as required, return an empty array.

Example 1:

Input: message = "this is really a very awesome message", limit = 9
Output: ["thi<1/14>","s i<2/14>","s r<3/14>","eal<4/14>","ly <5/14>","a v<6/14>","ery<7/14>"," aw<8/14>","eso<9/14>","me<10/14>"," m<11/14>","es<12/14>","sa<13/14>","ge<14/14>"]
Explanation:
The first 9 parts take 3 characters each from the beginning of message.
The next 5 parts take 2 characters each to finish splitting message. 
In this example, each part, including the last, has length 9. 
It can be shown it is not possible to split message into less than 14 parts.

Example 2:

Input: message = "short message", limit = 15
Output: ["short mess<1/2>","age<2/2>"]
Explanation:
Under the given constraints, the string can be split into two parts: 
- The first part comprises of the first 10 characters, and has a length 15.
- The next part comprises of the last 3 characters, and has a length 8.

Constraints:

1 <= message.length <= 10⁴
message consists only of lowercase English letters and ' '.
1 <= limit <= 10⁴

Split Message Based on Limit

Hard

Capital One

1 view

Topics:

Strings

You are given a string, message, and a positive integer, limit.

You must split message into one or more parts based on limit. Each resulting part should have the suffix "<a/b>", where "b" is to be replaced with the total number of parts and "a" is to be replaced with the index of the part, starting from 1 and going up to b. Additionally, the length of each resulting part (including its suffix) should be equal to limit, except for the last part whose length can be at most limit.

The resulting parts should be formed such that when their suffixes are removed and they are all concatenated in order, they should be equal to message. Also, the result should contain as few parts as possible.

Return the parts message would be split into as an array of strings. If it is impossible to split message as required, return an empty array.

Example 1:

Input: message = "this is really a very awesome message", limit = 9
Output: ["thi<1/14>","s i<2/14>","s r<3/14>","eal<4/14>","ly <5/14>","a v<6/14>","ery<7/14>"," aw<8/14>","eso<9/14>","me<10/14>"," m<11/14>","es<12/14>","sa<13/14>","ge<14/14>"]
Explanation:
The first 9 parts take 3 characters each from the beginning of message.
The next 5 parts take 2 characters each to finish splitting message. 
In this example, each part, including the last, has length 9. 
It can be shown it is not possible to split message into less than 14 parts.

Example 2:

Input: message = "short message", limit = 15
Output: ["short mess<1/2>","age<2/2>"]
Explanation:
Under the given constraints, the string can be split into two parts: 
- The first part comprises of the first 10 characters, and has a length 15.
- The next part comprises of the last 3 characters, and has a length 8.

Constraints:

1 <= message.length <= 10⁴
message consists only of lowercase English letters and ' '.
1 <= limit <= 10⁴

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 is the maximum allowed length of a single message segment, including the suffix?
Can the input message be empty or null?
If the message cannot be split into valid segments (e.g., a single word exceeds the limit), what should the function return?
Should the segment numbers be zero-indexed or one-indexed?
Are there any characters that are disallowed in the message, and should I handle escaping them?

Brute Force Solution

Approach

The brute force approach to splitting a message involves checking every possible way to divide the message into parts that fit within the given limit. We explore all combinations until we find a valid split, or exhaust all options. It's like trying every single possibility.

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

First, consider splitting the message into just one part and check if it fits within the limit.
If it doesn't fit, try splitting it into two parts at every possible position. Check the length of each part.
If a two-part split works, we're done. If not, try splitting into three parts, again at every conceivable position.
Keep doing this, increasing the number of parts, and checking all the combinations until you find a split where every part fits within the limit.
If you go through all the possibilities up to splitting into as many parts as there are characters (splitting after each character) and still don't find a working split, then it is impossible to split the message.

Code Implementation

def split_message_brute_force(message, limit):
    message_length = len(message)

    # Iterate through the possible number of parts.
    for number_of_parts in range(1, message_length + 1):
        # Try all possible splits for the current number of parts.
        for split_indices in find_all_splits(message_length, number_of_parts):
            is_valid = True
            start_index = 0

            # Check if each part is within the limit.
            for end_index in split_indices:
                part = message[start_index:end_index]
                if len(part) > limit:
                    is_valid = False
                    break
                start_index = end_index

            # Check the last part if needed
            if is_valid:
                last_part = message[start_index:]
                if len(last_part) > limit:
                    is_valid = False

            # If split is valid, return it
            if is_valid:
                result = []
                start_index = 0
                for end_index in split_indices:
                    result.append(message[start_index:end_index])
                    start_index = end_index
                result.append(message[start_index:])
                return result

    return None

def find_all_splits(message_length, number_of_parts):
    if number_of_parts == 1:
        yield []
        return

    # Recursively build the splits
    for i in range(1, message_length - number_of_parts + 2):
        for sub_split in find_all_splits(message_length - i, number_of_parts - 1):
            yield [i] + [i + x for x in sub_split]

Try it yourself on LeetCode

Big(O) Analysis

Time Complexity

O(n!) – The algorithm explores all possible splits of the message. In the worst case, we might need to try splitting the message into 1 part, then 2 parts, then 3 parts, and so on, up to n parts, where n is the length of the message. For splitting into k parts, there are approximately n choose (k-1) ways to do it. Summing this over all k from 1 to n involves calculating combinations, leading to a factorial-like growth in the number of combinations checked. Therefore, the time complexity is approximately O(n!).

Space Complexity

O(N) – The algorithm explores splitting the message into an increasing number of parts. In the worst-case scenario, it might need to store substrings of the message as it checks if they fit within the limit. The storage of these substrings, especially when considering splits into many parts, can require auxiliary space proportional to the length of the input message. Therefore, the auxiliary space complexity is O(N), where N is the length of the message. This is because, in the worst-case, we might store almost the entire message in smaller parts.

Optimal Solution

Approach

The goal is to break a long message into smaller parts, each fitting within a character limit, including an indicator showing its position. The key is to efficiently determine the space needed for the indicator and then divide the original message accordingly, taking care to handle potential edge cases.

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

First, figure out the maximum possible length of the indicator that will be attached to each piece of the message (e.g., '(1/99)'). Consider a few possibilities to be sure.
Subtract that maximum indicator length from the overall character limit to find out how much space is available for the actual message content in each piece.
Next, determine the total number of pieces the message will be split into based on the length of the original message and the space available for message content in each piece.
Now that you know how many pieces you'll have, split the original message into those pieces, making sure each piece does not exceed the allowable space. Use string slicing to accomplish this
For each piece, create the indicator with the current piece number and the total number of pieces, and attach it to the end of the message piece.
If at any point it's impossible to split the message because the message itself contains a word that is longer than the allowed length after adjusting for the indicator length, return an empty message.
Finally, combine all of the pieces and return the result.

Code Implementation

def split_message(message, limit):
    maximum_indicator_length = len(f'({1}/{999})')
    available_message_length = limit - maximum_indicator_length

    if available_message_length <= 0:
        return []

    number_of_parts = (len(message) + available_message_length - 1) // available_message_length

    # Check to prevent exceeding the number of parts
    if number_of_parts > 999:
        return []

    result = []
    start_index = 0

    # Split the message into smaller parts
    for part_number in range(1, number_of_parts + 1):
        end_index = min(start_index + available_message_length, len(message))
        message_part = message[start_index:end_index]

        # Check for words exceeding the limit.
        if any(len(word) > available_message_length for word in message_part.split()):
            return []

        indicator = f'({part_number}/{number_of_parts})'
        result.append(message_part + indicator)
        start_index = end_index

    return result

Try it yourself on LeetCode

Big(O) Analysis

Time Complexity

O(n) – The algorithm iterates through the input message of length n once to split it into chunks. Calculating the number of parts and constructing the indicators involves operations proportional to the number of chunks, which is at most n (when the message is split into single-character pieces after considering the indicator overhead). Therefore, the time complexity is primarily driven by the single pass through the input string, resulting in O(n) time complexity.

Space Complexity

O(N) – The algorithm creates a list to store the split message parts. In the worst-case scenario, where the message needs to be split into many small parts, the space required to store this list scales linearly with the length of the original message N. The indicator strings created for each split message also contribute to the overall space usage, proportional to the number of splits and thus related to N. Therefore, the auxiliary space complexity is O(N).

Edge Cases

Case	How to Handle
Null or empty message	Return an empty list or throw an IllegalArgumentException if the message is null or empty as there's nothing to split.
Limit is zero or negative	Throw an IllegalArgumentException if the limit is zero or negative because splitting is impossible.
Message length equals the limit exactly	Return a list containing only the original message, properly formatted with pagination.
Message length is slightly less than the limit but the pagination overhead makes it unsplittable	Return an empty list or throw an exception indicating that the message cannot be split under these constraints.
Very long message exceeding maximum reasonable number of segments	Implement a check for the maximum number of allowable segments to prevent excessive memory usage or potential integer overflow in pagination calculations and return an appropriate error.
Message containing special characters that might affect the length calculation or encoding	Ensure the character encoding is consistent (e.g., UTF-8) and the length calculation correctly accounts for multi-byte characters, by standardizing the length calculation method.
The overhead of (x/y) exceeds the limit, rendering the message unsplittable	Calculate the pagination overhead and reject messages where the overhead exceeds the available limit, providing a specific error message.
Message contains only delimiters or whitespace that are significant, creating empty messages.	Handle these edge cases by filtering out empty strings or whitespace-only strings after splitting, or by collapsing whitespace before splitting.