【LeetCode】Generate Parentheses

题目描述：

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:

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

要生成括号数为n的所有组合，可以对n-1的每个字符串从最低位到最高位插入"()"，用set去重，不过这样重复很多。

class Solution {
public:
	unordered_set<string> dup;
	vector<string> generateParenthesis(int n) {
		if (n == 1)
			return vector<string>(1,"()");
		vector<string> res;
		vector<string> s = generateParenthesis(n - 1);
		for (int i = 0; i < s.size(); i++){
			for (int j = 0; j <= s[i].length(); j++){
				string temp = s[i];
				temp = temp.insert(j, "()");
				if (dup.count(temp))
					continue;
				res.push_back(temp);
				dup.insert(temp);
			}
		}
		return res;
	}
};

还有关于卡特兰数的方法 看这里，学习中……