Generate Parentheses

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

For example, given n = 3, a solution set is:

"((()))", "(()())", "(())()", "()(())", "()()()"

也许是因为简单，这次的思路很清晰。

class Solution {
private:
    vector<string> res;
    string  str;
    int left=0;
    int right=0;
public:
    bool isValid(const char Par,int Pnum)
    {
        if(Par=='(')
        {
            if(left<Pnum)
                return true;
            else
                return false;
        }
        else 
        {
            if(right<left)
                return true;
            else
                return false;
        }
       /* if(left<Pnum&&right<left)
            return true;
        else
            return false;
            */
    }
    void getSolution(int flag,int Pnum)
    {
        if(flag==2*Pnum)
        {
            res.push_back(str);
            return;
        }
        
        if(isValid('(',Pnum))
        {
            str.append("(");
            left++;
            getSolution(flag+1,Pnum);
            str.pop_back();
            left--;
        }
        if(isValid(')',Pnum))
        {
            str.append(")");
            right++;
            getSolution(flag+1,Pnum);
            str.pop_back();
            right--;
        }
    }
    vector<string> generateParenthesis(int n) {
      getSolution(0,n);
      return res;
    }
};