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, orIt can be written as AB (A concatenated with B), where A and Bare valid strings, orIt 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: 1Example 2:
Input: "(((" Output: 3Example 3:
Input: "()" Output: 0Example 4:
Input: "()))((" Output: 4
Note:
S.length <= 1000S only consists of '(' and ')' characters.-------------------------------------------------------------------------------------------------------------------------------
这个题是栈的基础题,不过可以用O(n)的时间复杂度和O(1)的空间复杂度来解这个问题。参考题解:https://leetcode.com/articles/minimum-add-to-make-parentheses-valid/
C++代码:
class Solution { public: int minAddToMakeValid(string S) { int ans = 0,bal = 0; for(int i = 0; i < S.size(); i++){ bal += S[i] == '('?1:-1; if(bal == -1){ ans++; bal++; } } return ans+bal; } };
转载于:https://www.cnblogs.com/Weixu-Liu/p/10822557.html