🦄 Caesar Cipher: Rotate Letters

Difficulty: Beginner Tags: strings, cipher, modular arithmetic Series: CS 101

Problem

Implement a Caesar cipher - one of the oldest and simplest encryption techniques!

Your task: shift each lowercase letter in a string by k positions in the alphabet. When you reach 'z', wrap around back to 'a'. Leave all non-letter characters (spaces, punctuation, numbers) unchanged.

Input

data = {'text': str, 'k': int}

• text: The string to encrypt
• k: How many positions to shift (0-25)

Output

str  # The encrypted text

Constraints

• 0 ≤ k < 26 (shift amount)
• Text length ≤ 100,000 characters
• Only shift lowercase letters (leave everything else unchanged)

Examples

Example 1: Basic Shift

Input:  {'text': 'abc xyz!', 'k': 2}
Output: 'cde zab!'

Step-by-step: - 'a' + 2 = 'c' - 'b' + 2 = 'd' - 'c' + 2 = 'e' - ' ' stays ' ' (space) - 'x' + 2 = 'z' - 'y' + 2 = 'a' (wraps around!) - 'z' + 2 = 'b' (wraps around!) - '!' stays '!' (punctuation)

Example 2: Wrap-around

Input:  {'text': 'xyz', 'k': 3}
Output: 'abc'

Why? - 'x' is the 24th letter → shift by 3 → 27th position → wraps to 'a' (1st letter) - 'y' is the 25th letter → shift by 3 → 28th position → wraps to 'b' (2nd letter) - 'z' is the 26th letter → shift by 3 → 29th position → wraps to 'c' (3rd letter)

Example 3: Non-letters Unchanged

Input:  {'text': 'a-b', 'k': 1}
Output: 'b-c'

The hyphen '-' stays in place, only letters shift.