0022-generate-parentheses.cpp

/*
 Given n pairs of parentheses, generate all combos of well-formed parentheses
 Ex. n = 3 -> ["((()))","(()())","(())()","()(())","()()()"], n = 1 -> ["()"]

 Backtracking, keep valid, favor trying opens, then try closes if still valid

 Time: O(2^n)
 Space: O(n)
*/

classSolution {
public:
 vector<string> generateParenthesis(int n) {
 vector<string> result;
generate(n, 0, 0, "", result);
return result;
 }
private:
voidgenerate(int n, int open, int close, string str, vector<string>& result) {
if (open == n && close == n) {
 result.push_back(str);
return;
 }
if (open < n) {
generate(n, open + 1, close, str + '(', result);
 }
if (open > close) {
generate(n, open, close + 1, str + ')', result);
 }
 }
};