[leetcode]Generate Parentheses

题目：

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:

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

链接：https://oj.leetcode.com/problems/generate-parentheses/

描述：生成包含n对括号的所有合法括号序列

解法：dfs

solution by python:

class Solution:    # @param an integer    # @return a list of string    def generateParenthesis(self, n):        ans = []        self.generatePar(n,0,0,'',ans)        return ans    def generatePar(self,n, l, r, cur, ans):        if l==n and r==n:            ans.append(cur)            return        if l>r: self.generatePar(n,l,r+1,cur+')',ans)        if l<n: self.generatePar(n,l+1,r,cur+'(', ans)

solution by c++:

class Solution {public:    vector<string> generateParenthesis(int n) {        vector<string> ans;        dfs(0, n*2, 0, "", ans);        return ans;    }    void dfs(int cur, int n, int left, string par, vector<string> &ans){        if(cur >= n){            if(left == 0)                ans.push_back(par);            return;        }        dfs(cur+1, n, left+1, par+'(', ans);        if(left > 0)            dfs(cur+1, n, left-1, par+')', ans);    }};