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3614. Process String with Special Operations II

Description

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.

Solutions

Solution 1

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