Leetcode: Generate Parentheses @Python

class Solution:
    # @param an integer
    # @return a list of string
    def recurGen(self,l,r,rst,crt):
        if l==r==0:
            rst.append(crt)
            return
        if l>0:
            self.recurGen(l-1,r,rst,crt+'(')
        if r>l:
            self.recurGen(l,r-1,rst,crt+')')
            
    def generateParenthesis(self, n):
        rst=[]
        self.recurGen(n,n,rst,'')
        return rst