Generate Parentheses(C++)

givennpairs of parentheses, write a function to generate all combinations of well-formed parentheses.

class solution {

public:

vector generateparenthesis(int n)

{

vector ret;

findall(n,n,"",ret);

return ret;

}

void findall(int left,int right,string out,vector &ret)

{

if(left>right)

return;

if(left==0&&right==0)

return ret.push_back(out);

else

{

if(left>0)

findall(left-1,right,out+'(',ret);

if(right>0)

findall(left,right-1,out+')',ret);

}

}

};