Minimum String Length After Removing Substrings

class Solution {
public:
    int reduceLength(string str) {
        int position = 0;
        vector<char> temp(str.begin(), str.end());
    
        for (int index = 0; index < str.length(); index++) {
            temp[position] = temp[index];
    
            if (position > 0 &&
                (temp[position - 1] == 'A' || temp[position - 1] == 'C') &&
                temp[position] == temp[position - 1] + 1) {
                position--;
            } else {
                position++;
            }
        }
    
        return position;
    }
};

The provided C++ solution aims to minimize the length of a string by removing certain substrings according to specific rules. The function reduceLength processes a string by iterating over its characters, leveraging a two-pointer approach (utilizing index and position as pointers). Here's a concise breakdown of the approach:

• Initialize position to zero. This serves as the effective "current length" of the string being built.
• Convert the input string into a vector of characters, temp, for efficient modification.
• Iterate through the characters of temp. During each iteration:
  • Directly assign the character at index to temp[position].
  • Check if the current character can form a consecutive sequence (A with B, B with C, etc.) with the previous character.
  • If such a sequence is detected (temp[position] is consecutive to temp[position - 1]), decrement position to effectively remove the last character added.
  • If no sequence is detected, increment position to accept the current character.
• Return the value of position which represents the length of the string after consecutive sequences have been removed.

This solution efficiently removes pairs of consecutive letters, minimizing the length of the string without explicitly deleting elements from the original string, thus maintaining a lower time complexity. The final result after all possible reductions is the length of the new string.

class Solution {
    
    public int shortestLength(String str) {
        int outputIndex = 0;
        char[] letters = str.toCharArray();
    
        for (int inputIndex = 0; inputIndex < str.length(); inputIndex++) {
            letters[outputIndex] = letters[inputIndex];
    
            if (
                outputIndex > 0 &&
                (letters[outputIndex - 1] == 'A' ||
                    letters[outputIndex - 1] == 'C') &&
                letters[outputIndex] == letters[outputIndex - 1] + 1
            ) {
                outputIndex--;
            } else {
                outputIndex++;
            }
        }
    
        return outputIndex;
    }
}

In solving the problem of determining the minimum string length after removing specific substrings, the Java solution involves simulating the process of shortening a given string by selectively omitting certain characters under specific conditions. This method operates by maintaining an output length counter and modifying the string in place.

• Start by converting the input string into a character array for in-place modifications.
• Iterate through the array using a for-loop.
• Assign characters from the input index to the current position of what is tracked by the output index.
• The critical condition checks whether the previous character in the array is 'A' or 'C', and if the current character is directly subsequent to one of these in the ASCII table. If both conditions are met, decrement the output index, effectively removing the character pair from consideration.
• If the condition is not met, simply move the output index forward to consider the next character.

By the end of the loop, outputIndex reflects the length of the final string after all possible pairs have been removed. This value is then returned as the result. This solution optimizes by working directly on the input string’s character array, ensuring a more efficient and quicker algorithm without needing additional memory for other strings or data structures.

class Solution:
    def filterStringLength(self, input_str: str) -> int:
        char_array = list(input_str)
        output_index = 0
    
        for current_index in range(len(input_str)):
            char_array[output_index] = char_array[current_index]
    
            if (
                output_index > 0
                and char_array[output_index - 1] in "AC"
                and ord(char_array[output_index])
                == ord(char_array[output_index - 1]) + 1
            ):
                output_index -= 1
            else:
                output_index += 1  # No deletion needed, increment the index
    
        return output_index

The provided Python code defines a method filterStringLength within a Solution class, aimed at reducing the length of an input string by removing specific substrings. Here's how the method processes the input string:

• It converts the string to a list to manipulate the characters easily.
• The characters are processed one at a time using their positions in the list.
• The function checks for specific characters ('A' and 'C') followed by their immediate successors in the ASCII sequence (i.e., 'B' after 'A' and 'D' after 'C').
• When such sequences are found, the code effectively removes (does not copy) the successor character by not advancing in the output list.
• If no such condition is met, the character from the current position is maintained, and the output index is advanced.

This approach emphasizes an in-place modification of the character array, using output_index to control the length and content of the final output. The returned output_index indicates the effective length of the string after all possible removals have happened, reflecting the characters that pass the specified conditions. This method helps in optimizing the length of the string by removing unwanted subsequences, which aligns with string manipulation and optimization tasks in programming.