Zigzag Conversion

class Solution {
public:
    string zigzagConversion(string str, int rowCnt) {
        if (rowCnt == 1) {
            return str;
        }
    
        string transformedStr;
        int length = str.length();
        int cycleLen = 2 * (rowCnt - 1);
    
        for (int r = 0; r < rowCnt; ++r) {
            int pos = r;
    
            while (pos < length) {
                transformedStr += str[pos];
    
                if (r != 0 && r != rowCnt - 1) {
                    int middleCharPos = cycleLen - 2 * r;
                    int nextPos = pos + middleCharPos;
    
                    if (nextPos < length) {
                        transformedStr += str[nextPos];
                    }
                }
                pos += cycleLen;
            }
        }
    
        return transformedStr;
    }
};

The provided C++ solution is designed to perform the Zigzag Conversion for a given string based on a specified number of rows. The function zigzagConversion accepts a string str and an integer rowCnt which indicates the number of rows in the zigzag pattern.

Here's a breakdown of how the function operates:

• If rowCnt equals 1, the function immediately returns the original string as no transformation is necessary.
• A new empty string transformedStr is initialized to collect the characters in their new zigzag order.
• The function calculates cycleLen, which represents the repeating pattern length and is computed as 2 * (rowCnt - 1).
• The outer loop iterates through the row positions from 0 to rowCnt - 1. For each row, the function calculates the characters that belong to that row using an inner loop.
• Inside the inner loop, the position of the character to be appended, pos, is adjusted based on the current row and the cycle length.
• If the current row is neither the first nor the last (i.e., it has potential characters in between the standard vertical placements), it calculates an extra character position nextPos which represents a character in the middle of the zigzag pattern between the verticals.
• Characters positioned at pos and nextPos are appended to transformedStr if they are within the string's length.
• The function repeats the process until it covers all characters from the input string and then returns the reordered string.

This reordering transforms the string into its zigzag pattern, and the resulting string is designed to reflect the visual representation of text as it would appear when written in a zigzag manner across the specified number of rows.

class Solution {
    public String transform(String input, int rows) {
        if (rows == 1) {
            return input;
        }
    
        StringBuilder result = new StringBuilder();
        int length = input.length();
        int cycleLen = 2 * (rows - 1);
    
        for (int row = 0; row < rows; ++row) {
            int pos = row;
    
            while (pos < length) {
                result.append(input.charAt(pos));
    
                if (row != 0 && row != rows - 1) {
                    int midPos = cycleLen - 2 * row;
                    int nextCharPos = pos + midPos;
    
                    if (nextCharPos < length) {
                        result.append(input.charAt(nextCharPos));
                    }
                }
                pos += cycleLen;
            }
        }
    
        return result.toString();
    }
}

The Zigzag Conversion problem transforms a given string into a zigzag pattern on a given number of rows, then reads the characters row by row to produce a final zigzagged string. The provided solution in Java effectively handles this conversion with several key operations:

• Initial Checks and Setup: If the number of rows is 1, the string remains unchanged. The function computes the cycle length, which determines how characters are picked and skipped.

• String Building: A StringBuilder is utilized for efficiency as strings in Java are immutable, and appending multiple strings together could be costly if using regular string concatenation.

• Character Processing: The function iterates over each row and determines which characters belong to it based on the current row and cycle length. Characters are appended to the result as they are encountered:

  • For characters in the middle rows, besides appending the character at the current position, another character is picked from a position determined by subtracting twice the row number from the cycle length, if it is within string bounds. This ensures that characters that form the "zigzag" are included.

• Returning the Result: After all rows are processed, the collected characters in the StringBuilder form the final zigzagged string which is then converted to a regular string and returned.

This structured approach ensures that the zigzag pattern is followed, and the string is read and returned correctly based on the specified number of rows. The code efficiently handles varying lengths and row specifications without unnecessary complexity.

const char* zigzag_conversion(char* input, int row_count) {
    if (row_count == 1) {
        return input;
    }
    
    int length = strlen(input);
    char* result = malloc((length + 1) * sizeof(char));
    int cycle_length = 2 * (row_count - 1);
    
    int result_idx = 0;
    for (int row = 0; row < row_count; row++) {
        int pos = row;
        while (pos < length) {
            result[result_idx++] = input[pos];
    
            if (row != 0 && row != row_count - 1) {
                int intermediate_index = cycle_length - 2 * row;
                int next_char_index = pos + intermediate_index;
    
                if (next_char_index < length) {
                    result[result_idx++] = input[next_char_index];
                }
            }
            pos += cycle_length;
        }
    }
    result[length] = '\0';
    return result;
}

The Zigzag Conversion function in C is designed to rearrange characters of a given string into a specific zigzag pattern across multiple rows. This function is particularly useful in scenarios where such a visual arrangement of text is necessary, for example in text processing or specific encodings. Here's how this function efficiently processes a string and its characters:

• Parameter Handling and Memory Allocation: Begin by checking if the row_count is one, in which case it simply returns the input as no rearrangement is needed. The function calculates the required length of the input string and allocates memory for the resultant string.

• Zigzag Transformation Logic: Establishes a cycle determined by the cycle_length, which is calculated based on row_count. The function processes characters row by row. It determines the character position in the original string and stores it in the resulting array. If the current row is neither the first nor the last, it calculates an intermediate index which points to another character in the input string that fits into the zigzag pattern for the current row. The process continues until all the characters are processed.

• Character Appending: For each row, starting from the current row's initial position, the function appends characters to the result string. It then checks if additional characters fitting the pattern exist and appends them accordingly. This is continued across all rows determined by row_count.

• Finalization: After all rows are processed, the resultant string is null-terminated, ensuring proper string formation ready for any subsequent operations or output.

In summary, through calculated indexing and efficient looping, this function manipulates string characters into a zigzag pattern, optimizing memory and processing time by directly indexing into the input and resultant strings without additional data structures. This approach offers a streamlined and effective solution for the zigzag conversion problem.

let zigzagConvert = function (str, numRows) {
    if (numRows == 1) {
        return str;
    }
    
    let result = "";
    let length = str.length;
    let cycleLength = 2 * (numRows - 1);
    
    for (let row = 0; row < numRows; ++row) {
        let position = row;
    
        while (position < length) {
            result += str[position];
    
            // Check for intermediate characters between zigzag pattern peaks.
            if (row != 0 && row != numRows - 1) {
                let intermediateIndex = cycleLength - 2 * row;
                let nextChar = position + intermediateIndex;
    
                if (nextChar < length) {
                    result += str[nextChar];
                }
            }
            // Move to the next cycle's same row position.
            position += cycleLength;
        }
    }
    
    return result;
};

The provided code is a JavaScript function named zigzagConvert that transforms an input string into a specific zigzag pattern and then reads it row by row. The zigzag pattern's depth is determined by the numRows parameter. This function is primarily useful when one needs to reorganize the data in a non-linear manner, which can be relevant for various text processing applications.

Here’s a breakdown of the solution:

• The function first checks if numRows is 1. In such a case, the zigzag pattern doesn’t alter the original string, hence it directly returns the input string str.
• Initialize an empty string result to store the final zigzag-ordered text.
• Calculate cycleLength, which defines the repeat pattern length in the string as 2 * (numRows - 1).
• Use nested loops, where the outer loop iterates through each row from top to bottom, and the inner loop positions and fetches characters belonging to the current row in the zigzag pattern.
• Add characters to result from the current position. If the character is not on the first or last row, calculate and potentially add an intermediate character that appears between the main column characters in the zigzag pattern.
• Increment the position to point to the next corresponding character in the next cycle of the zigzag pattern.
• After constructing the result string by combining all characters from each row in sequence, the function returns result.

This approach leverages indices manipulation to efficiently gather characters by simulating the zigzag pattern traversal without actually rearranging the string physically. This direct indexing is computationally efficient as it prevents unnecessary string operations.

class ZigzagConversion:
    def transform(self, text: str, lines: int) -> str:
        if lines == 1:
            return text
    
        result = []
        length = len(text)
        cycle_len = 2 * (lines - 1)
    
        for row in range(lines):
            pos = row
            while pos < length:
                result.append(text[pos])
    
                if row != 0 and row != lines - 1:
                    mid_char_index = cycle_len - 2 * row
                    diagonal_index = pos + mid_char_index
    
                    if diagonal_index < length:
                        result.append(text[diagonal_index])
                            
                # Advance to the next equivalent position in the following cycle
                pos += cycle_len
    
        return "".join(result)

The Python code provided defines a class ZigzagConversion with a method transform aimed at converting a given string into a zigzag pattern across a given number of rows, then reading this pattern row by row.

The method starts by handling the simplest case where the number of lines is one. In this scenario, the text doesn't need any rearrangement, so it directly returns the input text.

• For more than one line, it initializes an empty list to hold characters in the zigzag order.
• It calculates the cycle_len which dictates the cycle of characters in a full vertical and diagonal traversal in the pattern.
• The outer loop iterates through the rows, and the inner loop handles each character placement in the result list:
  • It first adds characters vertically.
  • If the row isn't the first or the last, it also calculates and adds a character diagonally.
• The position to place the next character is updated by adding cycle_len to the current position.

Finally, it joins all characters in the result list into a single string, effectively transforming the text into its zigzag format and returns this string.