public static String caesarCipher(String s, int k) {
        char[] arr = "abcdefghijklmnopqrstuvwxyz".toCharArray(); // T(26) - > T(1)
        k %= arr.length;
          
        reverse(arr, 0, k - 1);
        reverse(arr, k, arr.length - 1 );
        reverse(arr, 0, arr.length - 1);
        //O(N)
        StringBuilder sb = new StringBuilder();
        //[c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z, a, b]
        for (int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);
            if (Character.isLetter(ch)) {
                if (Character.isLowerCase(ch)) {
                    int index = ch - 'a';
                    sb.append(arr[index]);
                } else {
                    int index = Character.toLowerCase(ch) - 'a';
                    sb.append(Character.toUpperCase(arr[index]));
                }
            } else {
                sb.append(ch);
            }
        }

        return sb.toString();
    }
    
    static void reverse(char[] arr, int start, int end) {
        while (start < end) {
            swap(arr, start, end);
            start++;
            end--;
        }
    }
    
    static void swap(char[] arr, int start, int end) {
        char temp = arr[start];
        arr[start] = arr[end];
        arr[end] = temp;
    }