# 1541. Minimum Insertions to Balance a Parentheses String
###### tags: `Leetcode` `Medium` `Parentheses`
Link: https://leetcode.com/problems/minimum-insertions-to-balance-a-parentheses-string/
## 思路
和[0921. Minimum Add to Make Parentheses Valid](https://hackmd.io/BW_TqN0oTsq6f0gxlYxXHw)的思路差不多，用余量做
但差别在于要区分只有一个')'和有'))'的情况
## Code

class Solution {
    public int minInsertions(String s) {
        int left = 0;
        int ans = 0;
        for(int i=0; i<s.length(); i++){
            if(s.charAt(i)=='(') left++;
            else{
                if(i+1<s.length() && s.charAt(i+1)==')') i+=1;
                else ans++;
                if(left==0) ans++;
                else left--;
            }
        }
        ans += left*2;
        return ans;
    }
}