leetcode140

 class Solution(object):
     def wordBreak(self, s, wordDict):
         """
         :type s: str
         :type wordDict: Set[str]
         :rtype: List[str]
         """
         return findWords(0, len(s), s, wordDict, {})

 def findWords(start, end, s, wordDict, cache):
     if start in cache:
         return cache[start]
     cache[start] = []
     candidate = ''
     current = start
     while current < end:
         candidate += s[current]
         current += 1
         if candidate in wordDict:
             if current == end:
                 cache[start].append(candidate)
             else:
                 for x in findWords(current, end, s, wordDict, cache):
                     cache[start].append(candidate + ' ' + x)
     return cache[start]