process-string-with-special-operations-ii

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 kth 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:

i
s[i]
Operation
Current result

0
'a'
Append 'a'
"a"

1
'#'
Duplicate result
"aa"

2
'b'
Append 'b'
"aab"

3
'%'
Reverse result
"baa"

4
'*'
Remove the last character
"ba"

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

Example 2:

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

Output: "d"

Explanation:

i
s[i]
Operation
Current result

0
'c'
Append 'c'
"c"

1
'd'
Append 'd'
"cd"

2
'%'
Reverse result
"dc"

3
'#'
Duplicate result
"dcdc"

4
'*'
Remove the last character
"dcd"

5
'#'
Duplicate result
"dcddcd"

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

Example 3:

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

Output: "."

Explanation:

i
s[i]
Operation
Current result

0
'z'
Append 'z'
"z"

1
'*'
Remove the last character
""

2
'#'
Duplicate the string
""

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

Constraints:

1 <= s.length <= 105

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

0 <= k <= 1015

The length of result after processing s will not exceed 1015.

process-string-with-special-operations-ii

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