algoadvance

Given a string s, the task is to remove duplicate characters from s such that each character appears only once. The output should be the minimized length of the string after removing the duplicates.

Clarifying Questions

  1. Are the characters case-sensitive? - Yes, lowercase and uppercase characters should be treated differently.
  2. Do the characters need to remain in any specific order in the final string? - The order of the unique characters in the final string doesn’t matter, only the count of unique characters does.
  3. What should be the output if the input string is empty? - The output should be 0, as there are no characters in the string.

Strategy

To solve this problem, we can use a set data structure which inherently maintains unique elements. The basic approach can be broken down into these steps:

  1. Initialize an empty set to keep track of the unique characters.
  2. Iterate over each character in the string s and add it to the set.
  3. The size of the set (len(set)) will represent the number of unique characters, which is the answer.

The use of a set ensures that each character only appears once, automatically handling the removal of duplicates.

Code

def minimize_string_length(s: str) -> int:
    # Initialize a set to track unique characters
    unique_chars = set()
    
    # Add each character in the input string to the set
    for char in s:
        unique_chars.add(char)
    
    # The size of the set is the number of unique characters
    return len(unique_chars)

# Example usage:
print(minimize_string_length("abca"))  # Output: 3
print(minimize_string_length("abcabc"))  # Output: 3
print(minimize_string_length(""))  # Output: 0
print(minimize_string_length("aAaA"))  # Output: 2 (since 'a' and 'A' are different)

Time Complexity

The time complexity of this solution is O(n), where n is the length of the input string s. This is because we iterate through each character in the string once, and each set insertion operation is average O(1) time complexity.

The space complexity is also O(n) in the worst case, where all characters in the string are unique, and hence, the set will store n characters.

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