3039. Apply Operations to Make String Empty Medium

1/**
2 * [3039] Apply Operations to Make String Empty
3 *
4 * You are given a string s.
5 * Consider performing the following operation until s becomes empty:
6 * 
7 * 	For every alphabet character from 'a' to 'z', remove the first occurrence of that character in s (if it exists).
8 * 
9 * For example, let initially s = "aabcbbca". We do the following operations:
10 * 
11 * 	Remove the underlined characters s = "<u>a</u>a<u>bc</u>bbca". The resulting string is s = "abbca".
12 * 	Remove the underlined characters s = "<u>ab</u>b<u>c</u>a". The resulting string is s = "ba".
13 * 	Remove the underlined characters s = "<u>ba</u>". The resulting string is s = "".
14 * 
15 * Return the value of the string s right before applying the last operation. In the example above, answer is "ba".
16 *  
17 * <strong class="example">Example 1:
18 * 
19 * Input: s = "aabcbbca"
20 * Output: "ba"
21 * Explanation: Explained in the statement.
22 * 
23 * <strong class="example">Example 2:
24 * 
25 * Input: s = "abcd"
26 * Output: "abcd"
27 * Explanation: We do the following operation:
28 * - Remove the underlined characters s = "<u>abcd</u>". The resulting string is s = "".
29 * The string just before the last operation is "abcd".
30 * 
31 *  
32 * Constraints:
33 * 
34 * 	1 <= s.length <= 5 * 10^5
35 * 	s consists only of lowercase English letters.
36 * 
37 */
38pub struct Solution {}
39
40// problem: https://leetcode.com/problems/apply-operations-to-make-string-empty/
41// discuss: https://leetcode.com/problems/apply-operations-to-make-string-empty/discuss/?currentPage=1&orderBy=most_votes&query=
42
43// submission codes start here
44
45impl Solution {
46    pub fn last_non_empty_string(s: String) -> String {
47        String::new()
48    }
49}
50
51// submission codes end
52
53#[cfg(test)]
54mod tests {
55    use super::*;
56
57    #[test]
58    fn test_3039() {
59    }
60}
61