[leetcode]22. Generate Parentheses(Java)

https://leetcode.com/problems/generate-parentheses/#/description

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:

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

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package go.jacob.day719;import java.util.ArrayList;import java.util.List;public class Demo3 {List<String> res;public List<String> generateParenthesis(int n) {res = new ArrayList<String>();if (n <= 0)return res;generateParenthesis(n, "(", 2, 1);return res;}private void generateParenthesis(int n, String str, int left, int right) {//终止条件if (left > n && right > n) {res.add(str);return;}if (left > n)generateParenthesis(n, str + ")", left, right + 1);//左括号和右括号小用户最大值else if (right < left) {generateParenthesis(n, str + "(", left + 1, right);generateParenthesis(n, str + ")", left, right + 1);} else if (right == left)generateParenthesis(n, str + "(", left + 1, right);}}