Minimum Add to Make Parentheses Valid

Description

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.

 

Solution(javascript)

// O(n) time O(n) space
// const minAddToMakeValid = (S = '') => {
//   const isPair = (left, right) => left === '(' && right === ')'
//   const stack = []
//   for (const c of S) {
//     if (isPair(stack[stack.length - 1], c)) {
//       stack.pop()
//     } else {
//       stack.push(c)
//     }
//   }
//   return stack.length
// }


const minAddToMakeValid = (S = '') => {
  let left = 0
  let right = 0
  for (let i = 0; i < S.length; i++) {
    if (S[i] === '(') {
      left += 1
    } else if (S[i] === ')') {
      if (left > 0) {
        left -= 1
      } else {
        right += 1
      }
    }
  }
  return left + right
}