Approach

To answer the interview question, "How would you replace all spaces in a string with '%20', given that the string has enough trailing space to accommodate the changes?", follow a structured framework that includes the following steps:

1. Understand the Problem: Clarify the requirements and constraints of the problem.

2. Identify the Method: Choose an efficient method for string manipulation.

3. Outline the Solution: Describe the algorithm and its implementation.

4. Consider Edge Cases: Discuss how to handle potential edge cases in the input.

5. Provide a Code Example: Illustrate the solution with a clear code snippet.

6. Explain the Complexity: Analyze the time and space complexity of the solution.

Key Points

• Clarity on Requirements: The string must have enough trailing space to fit the additional characters from replacements.

• Focus on Efficiency: Aim for a solution that minimizes additional space usage and operates within linear time complexity.

• Demonstrate Problem-Solving Skills: Show your ability to break down problems and arrive at a logical solution.

Standard Response

To replace all spaces in a string with '%20', we can follow these steps:

• Understand the String: We have a string that may contain spaces, and we are tasked with replacing each space with '%20'.

• Count Spaces: First, we need to count the number of spaces in the original string. This will help us determine how much extra space we need.

• Create a New String: Using the count of spaces, we can create a new string with enough additional space.

• Replace Spaces: We iterate through the original string, copying characters to the new string and replacing spaces with '%20'.

Here’s the Python code to accomplish this:

def replace_spaces(s: str) -> str:
 # Count spaces in the original string
 space_count = s.count(' ')
 
 # Calculate new length
 new_length = len(s) + space_count * 2 # Each space becomes '%20'
 
 # Create a list to hold new characters (immutable strings)
 new_chars = [''] * new_length
 index = new_length - 1 # Start filling from the end

 # Fill the new character array
 for i in range(len(s) - 1, -1, -1):
 if s[i] == ' ':
 new_chars[index] = '0'
 new_chars[index - 1] = '2'
 new_chars[index - 2] = '%'
 index -= 3
 else:
 new_chars[index] = s[i]
 index -= 1

 return ''.join(new_chars)

# Example usage
original_string = "Mr John Smith "
result = replace_spaces(original_string)
print(result) # Output: "Mr%20John%20Smith"

Tips & Variations

Common Mistakes to Avoid

• Ignoring Trailing Spaces: Ensure that the string has enough trailing spaces to accommodate the replacements.

• Inefficient String Concatenation: Avoid using string concatenation in a loop, as it can lead to excessive time complexity.

• Not Considering Edge Cases: Handle cases where the string may be empty or contain no spaces.

Alternative Ways to Answer

• Using Built-in Functions: In some programming languages, you can utilize built-in functions for string manipulation, but explaining the algorithm shows deeper understanding.

• Using Regular Expressions: For languages that support regex, this could be a compact solution, but it may not be as efficient.

Role-Specific Variations

• Technical Roles: Focus on the algorithm's efficiency, time, and space complexity.

• Managerial Roles: Discuss how you would guide your team in solving similar problems collaboratively.

• Creative Roles: Emphasize the importance of clean coding practices and readability.

Follow-Up Questions

• How would you handle strings that contain special characters?

• What would you do if the input string was very large?

• Can you explain how your solution could be optimized further?

• How would you implement this in a language that does not have built-in string manipulation tools?

This structured approach to answering the interview question not only demonstrates your technical skills but also your ability to communicate complex solutions clearly and effectively. By following this guide, job seekers can prepare to tackle similar coding challenges in their interviews, ensuring they present strong, well-thought-out responses