Split Message Based on Limit

Split Message Based on Limit

What is this problem about?

The Split Message Based on Limit coding problem is a challenging string task where you must take a long message and split it into several parts to fit within a specific character limit. However, there's a catch: each part must end with a suffix like <1/10>, <2/10>, etc. This suffix counts toward the character limit. Since the length of the suffix depends on the total number of parts (e.g., <1/9> is shorter than <1/10>), the problem becomes non-trivial because the total number of parts is initially unknown.

Why is this asked in interviews?

This "Hard" problem is popular at companies like Databricks and Uber because it requires a combination of Binary Search, Enumeration, and careful String manipulation. It tests whether a candidate can handle interdependent variables (message length per part and total parts). It's a great test of how you handle complex constraints and your ability to optimize a search space.

Algorithmic pattern used

The most common Algorithmic pattern used is Enumeration or Binary Search on the total number of parts. Since the total number of parts can't be huge (it's bounded by the message length), we can try possible values for the total number of parts, $T$. For a fixed $T$, we calculate the total capacity available for the message across all $T$ parts after accounting for the suffixes. The first $T$ that can accommodate the entire message is our answer.

Example explanation (use your own example)

Suppose your message is "Hello World" and the limit is 10. If we try 2 parts ($T=2$): Part 1 suffix is <1/2> (5 chars). Remaining for message: $10 - 5 = 5$ chars. Part 2 suffix is <2/2> (5 chars). Remaining for message: $10 - 5 = 5$ chars. Total message capacity = $5 + 5 = 10$ chars. "Hello World" is 11 chars. So $T=2$ is not enough. If we try 3 parts ($T=3$): Suffixes are <1/3>, <2/3>, <3/3> (all 5 chars). Total capacity = $5 + 5 + 5 = 15$. 15 is enough for 11 chars! The message is then split into "Hello", " Worl", and "d".

Common mistakes candidates make

• Ignoring suffix length changes: Not realizing that <1/9> is 5 characters while <1/10> is 6 characters.
• Overestimating parts: Trying to split the message without considering that the suffix length itself grows as the number of parts reaches powers of 10.
• Inefficient searching: Not realizing that the total capacity is monotonic with respect to the number of parts, allowing for faster search.
• Character count errors: Miscalculating the total length of all suffixes for a given $T$.

Interview preparation tip

When a variable $X$ depends on another variable $Y$, and $Y$ is also influenced by $X$, try fixing one variable and checking the feasibility of the other. This Split Message Based on Limit interview question is a classic example of where enumerating one variable simplifies the entire problem.