Using Dyck Path to solve a leetcode puzzle

Background

class Solution:
    def generateParenthesis(self, n):
        L = []
        if n==0:
            return ['']
        else:
            for i in range(1,n+1):
                s = map(lambda x: "("+x+")", self.generateParenthesis(i-1))
                for j in s:
                    L = L + list(map(lambda x: j+x, self.generateParenthesis(n-i)))
            return L