【回溯】22. Generate Parentheses

class Solution {
public:
    vector<string> generateParenthesis(int n) {

    	int left=0,right=0;
    	vector<string> ans;
    	string temp;

    	generate(ans,temp,left,right,n);
    	return ans;       
    }

    void generate(vector<string> &ans,string temp,int left,int right,int n)
    {
    	if(left==n&&right==n)
    	{
    		ans.push_back(temp);
    		return ;
    	}
    	
		
		if(left>right&&left<n)
		{
			temp +='(';
			left++;
			generate(ans,temp,left,right,n);	

			temp.erase(temp.size()-1,1);
			left--;

			temp +=')';		
			right++;			
			generate(ans,temp,left,right,n);
		}
		else
			if(left==right)
			{
				temp += '(';
				left++;
				generate(ans,temp,left,right,n);	
			}
			else
				if(left>right&&left==n)
				{
					temp += ')';
					right++;
					generate(ans, temp, left, right, n);
				}	
				else
					if (left < right)
						return;			
    }
};