leetcode-1021-remove-outermost-parentheses

A valid parentheses string is either empty (""), "(" + A + ")", or A + B, where A and B are valid parentheses strings, and + represents string concatenation. For example, "", "()", "(())()", and "(()(()))" are all valid parentheses strings.

A valid parentheses string S is primitive if it is nonempty, and there does not exist a way to split it into S = A+B, with A and B nonempty valid parentheses strings.

Given a valid parentheses string S, consider its primitive decomposition: S = P_1 + P_2 + … + P_k, where P_i are primitive valid parentheses strings.

Return S after removing the outermost parentheses of every primitive string in the primitive decomposition of S.

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class Solution {
public:
    string removeOuterParentheses(string S) {
        string result;

        int left = 0;
        for(int i = 0; i < S.length(); i++)
        {
            if(S[i] == '(')
            {
                if(left != 0)
                {
                    result += '(';
                }
                left++;
            }

            if(S[i] == ')')
            {
                left--;
                if(left != 0)
                {
                    result += ')';
                }
            }
        }

        return result;
    }
};