algoadvance

Given a string, the task is to count the number of special characters present in the string. A special character is any character that is not an alphabet (both uppercase and lowercase) or a digit (‘0’-‘9’).

Clarifying Questions

  1. Can the input string be empty?
    • Yes, in which case the result should be 0.
  2. What is the definition of special characters?
    • Any character that is not an English alphabet (A-Z, a-z) or a digit (0-9) is considered a special character.
  3. Are there any constraints on the length of the string?
    • Assume the length of the input string is reasonable and can fit in memory.
  4. Can the string contain Unicode characters?
    • For the sake of this problem, assume the string contains only ASCII characters.

Strategy

To solve this problem, we’ll use the following steps:

  1. Initialize a counter to keep track of the number of special characters.
  2. Iterate through each character in the string.
  3. Check if the character is a special character:
    • A character is a special character if it is not between ‘a’ and ‘z’, ‘A’ and ‘Z’, or ‘0’ and ‘9’.
  4. If the character is special, increment the counter.
  5. Return the counter as the result.

Code

Here is the Python code to solve the problem:

def count_special_characters(s: str) -> int:
    special_characters_count = 0
    
    for char in s:
        if not char.isalnum():
            special_characters_count += 1
    
    return special_characters_count

# Example usage:
if __name__ == "__main__":
    test_string = "Hello, World! 123"
    print(count_special_characters(test_string)) # Output: 4

Time Complexity

The time complexity of the solution is (O(n)), where (n) is the length of the string. This is because we are iterating through each character in the string once.

The space complexity is (O(1)) as we are using a constant amount of extra space regardless of the input size.

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