2075. Decode the Slanted Ciphertext
Description
A string originalText
is encoded using a slanted transposition cipher to a string encodedText
with the help of a matrix having a fixed number of rows rows
.
originalText
is placed first in a top-left to bottom-right manner.
![](https://spcdn.pages.dev/leetcode/problems/2075.Decode%20the%20Slanted%20Ciphertext/images/exa11.png)
The blue cells are filled first, followed by the red cells, then the yellow cells, and so on, until we reach the end of originalText
. The arrow indicates the order in which the cells are filled. All empty cells are filled with ' '
. The number of columns is chosen such that the rightmost column will not be empty after filling in originalText
.
encodedText
is then formed by appending all characters of the matrix in a row-wise fashion.
![](https://spcdn.pages.dev/leetcode/problems/2075.Decode%20the%20Slanted%20Ciphertext/images/exa12.png)
The characters in the blue cells are appended first to encodedText
, then the red cells, and so on, and finally the yellow cells. The arrow indicates the order in which the cells are accessed.
For example, if originalText = "cipher"
and rows = 3
, then we encode it in the following manner:
![](https://spcdn.pages.dev/leetcode/problems/2075.Decode%20the%20Slanted%20Ciphertext/images/desc2.png)
The blue arrows depict how originalText
is placed in the matrix, and the red arrows denote the order in which encodedText
is formed. In the above example, encodedText = "ch ie pr"
.
Given the encoded string encodedText
and number of rows rows
, return the original string originalText
.
Note: originalText
does not have any trailing spaces ' '
. The test cases are generated such that there is only one possible originalText
.
Example 1:
Input: encodedText = "ch ie pr", rows = 3 Output: "cipher" Explanation: This is the same example described in the problem description.
Example 2:
![](https://spcdn.pages.dev/leetcode/problems/2075.Decode%20the%20Slanted%20Ciphertext/images/exam1.png)
Input: encodedText = "iveo eed l te olc", rows = 4 Output: "i love leetcode" Explanation: The figure above denotes the matrix that was used to encode originalText. The blue arrows show how we can find originalText from encodedText.
Example 3:
![](https://spcdn.pages.dev/leetcode/problems/2075.Decode%20the%20Slanted%20Ciphertext/images/eg2.png)
Input: encodedText = "coding", rows = 1 Output: "coding" Explanation: Since there is only 1 row, both originalText and encodedText are the same.
Constraints:
0 <= encodedText.length <= 106
encodedText
consists of lowercase English letters and' '
only.encodedText
is a valid encoding of someoriginalText
that does not have trailing spaces.1 <= rows <= 1000
- The testcases are generated such that there is only one possible
originalText
.
Solutions
Solution 1
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