leetcode131 Palindrome Partitioning

"""
Given a string s, partition s such that every substring of the partition is a palindrome.
Return all possible palindrome partitioning of s.
Example:
Input: "aab"
Output:
[
  ["aa","b"],
  ["a","a","b"]
]
"""
"""
两个解法 ，一递归二迭代 都很难理解
"""
class Solution1:
    def partition(self, s):
        if not s:
            return [[]]
        path = []
        res = []
        self.dfs(s, path, res)
        return res

    def dfs(self, s, path, res):
        if not s:
            res.append(path)
        for i in range(1, len(s) + 1):  # 不理解,很难写
            pre = s[:i]
            if pre == pre[::-1]:
                self.dfs(s[i:], path + [pre], res)


class Solution2:
    def partition(self, s):
        """
        :type s: str
        :rtype: List[List[str]]
        """
        if not s:
            return []
        res = [[]]
        for i, x in enumerate(s):
            tmp = []
            for r in res:
                tmp.append(r + [x])
                if len(r) >= 1 and r[-1] == x:
                    tmp.append(r[:-1] + [r[-1] + x])

                if len(r) >= 2 and r[-2] == x:
                    tmp.append(r[:-2] + [r[-2] + r[-1] + x])

            res = tmp
        return res
if __name__ == '__main__':
    s = "aab"
    ans = Solution2()
    print(ans.partition(s))