problem

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

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 final string result after processing all characters in s.

 

Example 1:

Input: s = "a#b%*"

Output: "ba"

Explanation:

is[i]OperationCurrent 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"

Thus, the final result is "ba".

Example 2:

Input: s = "z*#"

Output: ""

Explanation:

is[i]OperationCurrent result
0'z'Append 'z'"z"
1'*'Remove the last character""
2'#'Duplicate the string""

Thus, the final result is "".

 

Constraints:

  • 1 <= s.length <= 20
  • s consists of only lowercase English letters and special characters *, #, and %.

submission

// simulate, boring
impl Solution {
    pub fn process_str(s: String) -> String {
        s.chars()
            .fold(String::new(), |mut res, ch| {
                match ch {
                    '*' => {
                        res.pop();
                    }
                    '#' => {
                        res.push_str(&res.clone());
                    }
                    '%' => {
                        res = res.chars().rev().collect();
                    }
                    ch => {
                        res.push(ch);
                    }
                }
                res
            })
    }
}