Question

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.

Difficulty:Medium

Category:

Analyze

Solution

class Solution {
 public:
  int minAddToMakeValid(string s) {
    int ans = 0;
    stack<char> sta;
    for (int i = 0; i < s.size(); ++i) {
      if (s[i] == '(')
        sta.push(s[i]);
      else {
        if (sta.empty()) {
          ans++;
          continue;
        } else if (s[i] == ')' && sta.top() != '(')
          ans++;
        sta.pop();
      }
    }
    ans += sta.size();
    return ans;
  }
};

Related Problems

• Valid Parentheses