[LeetCode]Generate Parentheses

Posted 2020-06-19 skycore

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:

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

解题思路：

基本想法是用递归，当左括号数 < n, 可以继续放左括号，当右括号数<左括号数时，可以继续放右括号。 

 1 class Solution {
 2 public:
 3     vector<string> generateParenthesis(int n) {
 4         vector<string> result;
 5         if (n > 0) {
 6             generateParenthesis(n, "", 0, 0, result);
 7         }
 8         
 9         return result;
10     }
11 private:
12     void generateParenthesis(int n, string s, int l, int r, vector<string> &result) {
13         if (l == n) {
14             result.push_back(s.append(n - r, ‘)‘));
15             return;
16         }
17         generateParenthesis(n, s + ‘(‘, l + 1, r, result);
18         
19         if (r < l) {
20            generateParenthesis(n, s + ‘)‘, l, r + 1, result); 
21         }
22     }
23 };