algoadvance

You are given a series of events that represent opening or closing a door using a key. Each event is represented by a string: “open” or “close”. You need to determine the number of times someone used a key during these events. Assume each event represents a single key usage, either to open or close the door.

Clarifying Questions

  1. Can the sequence of events start with a “close”?
  2. Are there any invalid sequences (e.g., multiple consecutive “open” without a “close”)?
  3. Is the sequence limited to “open” and “close” strings only?
  4. Should I consider “open” following “open” or “close” following “close” as an extra key usage?

For the sake of simplifying the problem, we’ll assume the sequence alternates correctly and starts with an “open”.

Strategy

  1. Iterate through the list of events.
  2. Count each “open” and “close” as it represents using a key.
  3. Return the count as the result.

Code

def number_of_key_usages(events):
    return len(events)

# Example usage
events = ["open", "close", "open", "close", "open", "close"]
print(number_of_key_usages(events))  # Output: 6

Time Complexity

The time complexity for this solution is O(1) for counting the length of the events list. This is because the len function is implemented in constant time in Python.

Edge Cases

  1. Empty List: If the input list is empty, the function should return 0.
  2. Non-alternating sequence: If the sequence doesn’t alternate correctly, the function still counts the number of keys used as it doesn’t check for validity as per the problem statement.

Try our interview co-pilot at AlgoAdvance.com