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Validate Password Against Multiple Rules

Otter.AiSoftware Engineer · Technical Screen
EasySoftware EngineerTechnical ScreenCoding & Algorithms

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This problem tests your ability to efficiently iterate through a string while maintaining multiple state-based flags to satisfy diverse validation criteria.

Validate Password Strength

Given a string password, implement a function that returns True if the password meets all the following security requirements, and False otherwise:

  1. Length: Must be between 8 and 20 characters, inclusive.
  2. Complexity: Must contain at least one uppercase letter, one lowercase letter, one digit, and one special character (from the set !@#$%^&*).
  3. Repetition: Must not contain three or more consecutive identical characters (e.g., "aaa" is invalid).

Function Signature

def is_valid_password(password: str) -> bool:

Examples

Example 1: Input: password = "Abc1!def" Output: True Explanation: Length is 8, contains all required character types, and no three consecutive identical characters exist.

Example 2: Input: password = "AAAbc123!" Output: False Explanation: Contains three consecutive 'A's, which violates the repetition rule.

Constraints

  • The string will contain only ASCII characters.
  • The password length is at most 100 characters.

Edge Cases

  • Empty strings or strings with length < 8.
  • Strings with characters outside the specified special set.
  • Strings with exactly 20 characters.

Hints

Hint 1

Check the length constraint first to return early if the password is too short or too long.

Hint 2

Use a set or a boolean flag for each complexity requirement and update them while iterating through the string once.

Hint 3

To check for three consecutive identical characters, maintain a counter or compare the current character with the two previous characters.

Follow-up questions

  • How would you modify your solution to allow a custom set of prohibited special characters?
  • If you needed to check against a large dictionary of banned passwords (e.g., '123456', 'password'), how would you optimize the validation?
  • How could you implement this using Regular Expressions, and what are the performance trade-offs compared to the iterative approach?