1249. Minimum Remove to Make Valid Parentheses

Given a string s of `'('` , `')'` and lowercase English characters.

Your task is to remove the minimum number of parentheses ( `'('` or `')'`, in any positions ) so that the resulting parentheses string is valid and return any valid string.

Formally, a parentheses string is valid if and only if:

• It is the empty string, contains only lowercase characters, or
• It can be written as `AB` (`A` concatenated with `B`), where `A` and `B` are valid strings, or
• It can be written as `(A)`, where `A` is a valid string.

Example 1:

```Input: s = "lee(t(c)o)de)"
Output: "lee(t(c)o)de"
Explanation: "lee(t(co)de)" , "lee(t(c)ode)" would also be accepted.
```

Example 2:

```Input: s = "a)b(c)d"
Output: "ab(c)d"
```

Example 3:

```Input: s = "))(("
Output: ""
Explanation: An empty string is also valid.
```

Example 4:

```Input: s = "(a(b(c)d)"
Output: "a(b(c)d)"
```

Constraints:

• `1 <= s.length <= 10^5`
• `s[i]` is one of  `'('` , `')'` and lowercase English letters`.`

1249. Minimum Remove to Make Valid Parentheses
``````struct Solution;

use std::collections::HashSet;

impl Solution {
fn min_remove_to_make_valid(s: String) -> String {
let mut stack: Vec<usize> = vec![];
let mut res: String = "".to_string();
let mut remove: HashSet<usize> = HashSet::new();
for (i, c) in s.char_indices() {
match c {
'(' => {
stack.push(i);
}
')' => {
if stack.pop().is_none() {
remove.insert(i);
}
}
_ => {}
}
}
for i in stack {
remove.insert(i);
}
for (i, c) in s.char_indices() {
if !remove.contains(&i) {
res.push(c);
}
}
res
}
}

#[test]
fn test() {
let s = "lee(t(c)o)de)".to_string();
let res = "lee(t(c)o)de".to_string();
assert_eq!(Solution::min_remove_to_make_valid(s), res);
let s = "a)b(c)d".to_string();
let res = "ab(c)d".to_string();
assert_eq!(Solution::min_remove_to_make_valid(s), res);
let s = "))((".to_string();
let res = "".to_string();
assert_eq!(Solution::min_remove_to_make_valid(s), res);
let s = "(a(b(c)d)".to_string();
let res = "a(b(c)d)".to_string();
assert_eq!(Solution::min_remove_to_make_valid(s), res);
}
``````