LeetCode 2075: Decode the Slanted Ciphertext Solution

Master LeetCode problem 2075 (Decode the Slanted Ciphertext), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

2075. Decode the Slanted Ciphertext

Medium

String Simulation

Problem Explanation

Explanation

To decode the slanted ciphertext, we will simulate the encoding process in reverse. We will iterate through the encoded text and fill the characters back into a matrix based on the given number of rows. By observing the pattern of how the characters were filled during encoding, we can reconstruct the original text.

Time complexity: O(n), where n is the length of the encoded text. Space complexity: O(n), where n is the length of the encoded text.

Solution Code

class Solution {
    public String decodeSlantedCiphertext(String encodedText, int rows) {
        if (rows == 1) {
            return encodedText;
        }
        
        int cols = (encodedText.length() + rows - 1) / rows;
        char[][] matrix = new char[rows][cols];
        int index = 0;
        
        for (int c = 0; c < cols; c++) {
            for (int r = 0; r < rows; r++) {
                if (c % 2 == 0 || r == rows - 1) {
                    matrix[r][c] = encodedText.charAt(index++);
                }
            }
        }
        
        StringBuilder originalText = new StringBuilder();
        for (int r = 0; r < rows; r++) {
            for (int c = 0; c < cols; c++) {
                if (matrix[r][c] != 0) {
                    originalText.append(matrix[r][c]);
                }
            }
        }
        
        return originalText.toString();
    }
}

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