The Minimum Number of Chairs in a Waiting Room coding problem is a simulation-based challenge. You are given a string representing the movements of people in a room. 'E' means someone enters, and 'L' means someone leaves. You need to determine the maximum number of people present in the room at any single point in time, as this represents the minimum number of chairs required to ensure everyone has a seat.
Companies like Amazon and Expedia use this question to evaluate a candidate's ability to translate a real-world scenario into a simple counter-based algorithm. It’s a test of "Stream Processing"—handling events one by one and maintaining a running state. It also checks if you can identify the "peak" of a fluctuating value, which is a fundamental concept in capacity planning and resource management.
The problem falls under the String, Simulation interview pattern. It doesn't require complex data structures like heaps or trees. Instead, it relies on a simple linear scan (O(n) time complexity). You maintain two variables: a current count of people and a maximum count seen so far. As you iterate through the string, you increment for 'E' and decrement for 'L', updating the maximum whenever the current count exceeds it.
Input String: "EEEL ELE" (ignoring spaces) -> "EEELLEL"
The most common mistake is overcomplicating the problem by trying to store the times or using a more complex data structure than necessary. Some candidates might forget to update the "maximum" variable at every step, or they might initialize the maximum to 0 and fail to handle cases where the room starts empty. Another minor error is confusing 'E' and 'L' logic if not reading the problem carefully.
When you encounter a problem that asks for "maximum capacity" or "peak usage," think of a simple counter. These problems are often easier than they look. Practice writing clean, concise loops and focus on variable naming to make your simulation logic immediately obvious to the interviewer.
