LeetCode22: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:

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

LeetCode:リンクりんく
左かっこに残りがある場合は左かっこ、右かっこの残りが左かっこより大きい場合は右かっこを配置できます.

class Solution(object):
    def generateParenthesis(self, n):
        """
        :type n: int
        :rtype: List[str]
        """
        if n == 0:
            return []
        res = []
        self.generate(n, n, "", res)
        return res

    # left        right        pStr          
    def generate(self, left, right, pStr, res):
        if left == 0 and right == 0:
            res.append(pStr)
            return
        #          ，        
        if left > 0:
            self.generate(left-1, right, pStr+"(", res)
        #               ，        
        if right > left:
            self.generate(left, right-1, pStr+")", res)