921. 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:

S.length <= 1000
S only consists of '(' and ')' characters.

Approach #1: C++.[stack]

class Solution {

public:

    int minAddToMakeValid(string S) {

        int len = S.length();

        if (len == 0) return 0;

        stack<char> myStack;

        myStack.push(S[0]);

        for (int i = 1; i < len; ++i) {

            if (myStack.empty()) myStack.push(S[i]);

            else if (myStack.top() == '(' && S[i] == ')') myStack.pop();

            else myStack.push(S[i]);

        }

        return myStack.size();

    }

};

巴特西

921. Minimum Add to Make Parentheses Valid

最新文章

热门文章