"""

给定一个非空字符串 s 和一个包含非空单词列表的字典 wordDict，在字符串中增加空格来构建一个句子，使得句子中所有的单词都在词典中。返回所有这些可能的句子。

说明：

分隔时可以重复使用字典中的单词。
你可以假设字典中没有重复的单词。
示例 1：

输入:
s = "catsanddog"
wordDict = ["cat", "cats", "and", "sand", "dog"]
输出:
[
  "cats and dog",
  "cat sand dog"
]
示例 2：

输入:
s = "pineapplepenapple"
wordDict = ["apple", "pen", "applepen", "pine", "pineapple"]
输出:
[
  "pine apple pen apple",
  "pineapple pen apple",
  "pine applepen apple"
]
解释: 注意你可以重复使用字典中的单词。
示例 3：

输入:
s = "catsandog"
wordDict = ["cats", "dog", "sand", "and", "cat"]
输出:
[]
"""
class Solution:
    def wordBreak(self, s, wordDict):
        """
        :type s: str
        :type wordDict: List[str]
        :rtype: List[str]
        """
        return self.traversal(s, wordDict, {})
    
    def traversal(self, s, wordDict, dic):
        
        if s in dic: return dic[s]
        if not s: return []
        
        res = []
        for key in wordDict:
            if not s.startswith(key):
                continue
            if len(s) == len(key):
                res.append(s)
            else:
                tmp = self.traversal(s[len(key):], wordDict, dic)
                for item in tmp:
                    res.append(key + ' ' + item)
        dic[s] = res
        return res