921. Minimum Add to Make Parentheses Valid

Given a string S of '(' and ')' parentheses, we add the minimum number of parentheses ( '(' or ')', and in any positions ) so that the resulting parentheses string is valid.

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

  • It is the empty string, 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.

Given a parentheses string, return the minimum number of parentheses we must add to make the resulting string valid.

 

Example 1:

Input: "())"
Output: 1

Example 2:

Input: "((("
Output: 3

Example 3:

Input: "()"
Output: 0

Example 4:

Input: "()))(("
Output: 4

 

Note:

  1. S.length <= 1000
  2. S only consists of '(' and ')' characters.
 

Rust Solution

struct Solution;

impl Solution {
    fn min_add_to_make_valid(s: String) -> i32 {
        let mut stack: Vec<char> = vec![];
        let mut res = 0;
        for c in s.chars() {
            match c {
                '(' => {
                    stack.push(c);
                }
                ')' => {
                    if stack.is_empty() {
                        res += 1;
                    } else {
                        stack.pop();
                    }
                }
                _ => {}
            }
        }
        res + stack.len() as i32
    }
}

#[test]
fn test() {
    let s = "())".to_string();
    let res = 1;
    assert_eq!(Solution::min_add_to_make_valid(s), res);
    let s = "(((".to_string();
    let res = 3;
    assert_eq!(Solution::min_add_to_make_valid(s), res);
    let s = "()".to_string();
    let res = 0;
    assert_eq!(Solution::min_add_to_make_valid(s), res);
    let s = "()))((".to_string();
    let res = 4;
    assert_eq!(Solution::min_add_to_make_valid(s), res);
}

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