Leetcode #2075: Decode the Slanted Ciphertext
In this guide, we solve Leetcode #2075 Decode the Slanted Ciphertext in Python and focus on the core idea that makes the solution efficient.
You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.
Problem Statement
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.
Quick Facts
- Difficulty: Medium
- Premium: No
- Tags: String, Simulation
Intuition
We need to scan characters while tracking positions or counts.
A simple state machine keeps the logic precise.
Approach
Iterate through the string once and update the state for each character.
Use a map or array if you need fast lookups.
Steps:
- Iterate through characters.
- Maintain necessary state.
- Build or validate the output.
Example
Input: encodedText = "ch ie pr", rows = 3
Output: "cipher"
Explanation: This is the same example described in the problem description.
Python Solution
class Solution:
def decodeCiphertext(self, encodedText: str, rows: int) -> str:
ans = []
cols = len(encodedText) // rows
for j in range(cols):
x, y = 0, j
while x < rows and y < cols:
ans.append(encodedText[x * cols + y])
x, y = x + 1, y + 1
return ''.join(ans).rstrip()
Complexity
The time complexity is , and the space complexity is , where is the length of the string . The space complexity is , where is the length of the string .
Edge Cases and Pitfalls
Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.
Summary
This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.