Alg.11 Caesar Cipher Encryptor

From algoexpert.io

This is a easy string-related problem, given a string and a number k, we need to shift every character in the string k positions in the alphabet list.

Basically, we iterate this string, get each expecting character after we shift k positions. According to the ASCII code, assume current character’s ASCII is c, the transformed ASCII is c - ‘a’ + k, then we get the remainder, answer will be ‘a’ + (c - ‘a’ + k) % (‘z’ - ‘a’ + 1).

Here is the code implementation:

public static String caesarCypherEncryptor(String str, int key) {
        StringBuilder ans = new StringBuilder();
        for (int i = 0; i < str.length(); i++) {
            int diff = str.charAt(i) - 'a' + key;
            int trans = diff % ('z' - 'a' + 1);
            char c = (char)(trans + 'a');
            ans.append(c);
        }
    return ans.toString();
  }

Time complexity: O(n); Space complexity: O(n)

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