#Leetcode# 22. Generate Parentheses

https://leetcode.com/problems/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:

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

代码：

class Solution {
public:
    vector<string> generateParenthesis(int n) {
        vector<string> ans;
        dfs(n, n, "", ans);
        return ans;
    }
    void dfs(int L, int R, string out, vector<string> &ans) {
        if(L > R) return;
        if(L == 0 && R == 0) ans.push_back(out);
        else {
            if(L > 0) dfs(L - 1, R, out + '(', ans);
            if(R > 0) dfs(L, R - 1, out + ')', ans);
        }
    }
};

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