Split a String in Balanced Strings

Split a String in Balanced Strings

What is this problem about?

The Split a String in Balanced Strings interview question focuses on the concept of balanced substrings. A string is "balanced" if it contains an equal number of 'L' and 'R' characters. Given a balanced string, the task is to split it into the maximum number of balanced substrings possible. This is a fundamental string manipulation problem that emphasizes the "greedy" approach to optimization.

Why is this asked in interviews?

This Split a String in Balanced Strings coding problem is a popular "easy" question at Meta, Amazon, and Google. It tests if a candidate can identify that a simple greedy choice—splitting as soon as a balance is reached—leads to the global optimum. It's an excellent way to assess basic logic and the ability to implement a solution with minimal time and space complexity ($O(n)$ time and $O(1)$ space).

Algorithmic pattern used

The Greedy interview pattern is perfect for this problem. You maintain a counter that increments for 'R' and decrements for 'L' (or vice versa). Every time the counter returns to zero, it means you have just completed a balanced substring. Because you want the maximum number of substrings, you should increment your total count and "split" the string immediately at that point.

Example explanation

String: RLRRLLRLRL

1. First char 'R': count = 1.
2. Second char 'L': count = 0. Balance! Substrings = 1.
3. Third char 'R': count = 1.
4. Fourth char 'R': count = 2.
5. Fifth char 'L': count = 1.
6. Sixth char 'L': count = 0. Balance! Substrings = 2.
7. Seventh char 'R': count = 1.
8. Eighth char 'L': count = 0. Balance! Substrings = 3.
9. Ninth char 'R': count = 1.
10. Tenth char 'L': count = 0. Balance! Substrings = 4. Total: 4 balanced substrings.

Common mistakes candidates make

• Overcomplicating the Logic: Trying to use dynamic programming or complex string slicing when a single counter is sufficient.
• Not Splitting Early: Thinking they need to look ahead to see if a different split would be better, failing to realize the greedy property of this specific problem.
• Initial Count: Starting the count at something other than zero or mis-handling the first character.
• Language-Specific Inefficiency: Creating many sub-string objects in memory instead of just counting the split points.

Interview preparation tip

Greedy problems often have a "no-regret" property. If you can prove that making a local optimal choice (like splitting as soon as balance=0) doesn't prevent you from making the best choices later, then Greedy is the way to go. Practice identifying these patterns to solve "maximum number of..." problems quickly.