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 withB
), whereA
andB
are valid strings, or - It can be written as
(A)
, whereA
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:
S.length <= 1000
S
only consists of'('
and')'
characters.
思路:
用一个栈即可,如果顶部和字符串中的当前字符匹配则出栈,最后栈的大小即为不匹配的个数。
int minAddToMakeValid(string S) { if(S.length()<=1)return S.length(); stack<char>st; for(int i = 0; i < S.length(); i++) { if(S[i] == ')' && !st.empty() && st.top() == '(') { st.pop(); continue; } else { st.push(S[i]); } } return st.size(); }