22. 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:

[  "((()))",  "(()())",  "(())()",  "()(())",  "()()()"]

思路：

深度优先算法。

public class Solution {    public List<String> generateParenthesis(int n) {        List<String> res = new ArrayList<String>();if (n <= 0)return res;String bracket = "";dfs(res, bracket, n, n);return res;    }        private void dfs(List<String> res, String bracket, int left,int right) {if(left > right){return;}if (left == 0 && right == 0) {res.add(bracket);return;}if (left > 0) {dfs(res, bracket + "(", left - 1, right);}if (right > 0) {dfs(res, bracket + ")", left, right - 1);}    }}