String Length Cases - codepath/compsci_guides GitHub Wiki

Unit 7 Session 1 (Click for link to problem statements)

Problem Highlights

  • 💡 Difficulty: Easy
  • ⏰ Time to complete: 10 mins
  • 🛠️ Topics: Recursion, String Manipulation

1: U-nderstand

Understand what the interviewer is asking for by using test cases and questions about the problem.

  • Established a set (2-3) of test cases to verify their own solution later.
  • Established a set (1-2) of edge cases to verify their solution handles complexities.
  • Have fully understood the problem and have no clarifying questions.
  • Have you verified any Time/Space Constraints for this problem?
  • Q: How should the function handle an empty string?
    • A: The function should return 0 for an empty string, indicating that it has no characters.
HAPPY CASE
Input: "hello"
Output: 5
Explanation: The string "hello" has 5 characters.

EDGE CASE
Input: ""
Output: 0
Explanation: An empty string has 0 characters.

2: M-atch

Match what this problem looks like to known categories of problems, e.g. Linked List or Dynamic Programming, and strategies or patterns in those categories.

This problem is a fundamental example of using recursion to solve simple computational problems:

  • Understanding recursion as breaking down a problem into smaller pieces.
  • Using recursion to iterate through a string one character at a time to count its length.

3: P-lan

Plan the solution with appropriate visualizations and pseudocode.

General Idea: Write a recursive function to calculate the length of a string by processing one character at a time.

1) Base Case: If the string is empty, return 0.
2) Recursive Case: Return 1 plus the recursive call for the substring starting from the second character.

⚠️ Common Mistakes

  • Not correctly identifying the base case, which could lead to an infinite recursion or incorrect counting.

4: I-mplement

Implement the code to solve the algorithm.

def string_length(s):
    if s == "":
        return 0
    else:
        return 1 + string_length(s[1:])

5: R-eview

Review the code by running specific example(s) and recording values (watchlist) of your code's variables along the way.

  • Trace through your code with input "hello" to ensure it correctly calculates the length as 5.
  • Validate the function with an empty string to confirm that it returns 0.

6: E-valuate

Evaluate the performance of your algorithm and state any strong/weak or future potential work.

  • Time Complexity: O(n) where n is the length of the string, since each recursive call processes one character.
  • Space Complexity: O(n) due to the recursion stack depth, which grows linearly with the length of the string.