Leetcode 2075. Decode the Slanted Ciphertext

Reverse a slanted transposition cipher: encodedText is produced by reading a rows×cols matrix row-by-row after originalText was placed along top-left-to-bottom-right diagonals (with spaces padded), so given encodedText and rows reconstruct the matrix and recover the original text by reading the characters along those diagonals (trimming trailing spaces).