3614 - Process String with Special Operations II.

Hard

You are given a string s consisting of lowercase English letters and the special characters: '*', '#', and '%'.

You are also given an integer k.

Build a new string result by processing s according to the following rules from left to right:

• If the letter is a lowercase English letter append it to result.

• A '*' removes the last character from result, if it exists.

• A '#' duplicates the current result and appends it to itself.

• A '%' reverses the current result.

Return the <code>k^th</code> character of the final string result. If k is out of the bounds of result, return '.'.

Example 1:

Input: s = "a#b%\*", k = 1

Output: "a"

Explanation:

The final result is "ba". The character at index k = 1 is 'a'.

Example 2:

Input: s = "cd%#\*#", k = 3

Output: "d"

Explanation:

The final result is "dcddcd". The character at index k = 3 is 'd'.

Example 3:

Input: s = "z\*#", k = 0

Output: "."

Explanation:

The final result is "". Since index k = 0 is out of bounds, the output is '.'.

Constraints:

• <code>1 <= s.length <= 10⁵</code>

• s consists of only lowercase English letters and special characters '*', '#', and '%'.

• <code>0 <= k <= 10¹⁵</code>

• The length of result after processing s will not exceed <code>10¹⁵</code>.