2075\. Decode the Slanted Ciphertext

Medium

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://assets.leetcode.com/uploads/2021/11/07/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://assets.leetcode.com/uploads/2021/11/07/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://assets.leetcode.com/uploads/2021/10/25/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://assets.leetcode.com/uploads/2021/10/26/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://assets.leetcode.com/uploads/2021/10/26/eg2.png)

**Input:** encodedText = "coding", rows = 1

**Output:** "coding"

**Explanation:** Since there is only 1 row, both originalText and encodedText are the same. 

**Constraints:**

*   <code>0 <= encodedText.length <= 10<sup>6</sup></code>
*   `encodedText` consists of lowercase English letters and `' '` only.
*   `encodedText` is a valid encoding of some `originalText` that **does not** have trailing spaces.
*   `1 <= rows <= 1000`
*   The testcases are generated such that there is **only one** possible `originalText`.