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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.

題目理解:

給定一個只含有左括號和右括號的陣列,判斷還需要新增多少個括號才能時得括號合法

解題思路:

分別找出無法匹配的左括號和無法匹配的右括號就可以了,注意")("這種情況是不能匹配的

程式碼如下:

class Solution {
    public int minAddToMakeValid(String S) {
        int a = 0, b = 0;
        for(char ch : S.toCharArray()){
            if(ch == '(')
                a++;
            else{
                if(a > 0)
                    a--;
                else
                    b++;
            }
        }
        return a + b;
    }
}