The code is self-explanatory.

Note that the Set membership test (s[j:i] in wordDict) in python is O(1).

```
class Solution(object):
def wordBreak(self, s, wordDict):
"""
:type s: str
:type wordDict: Set[str]
:rtype: bool
"""
dp = [False]*(len(s)+1)
dp[0] = True
for i in range(1, len(s)+1):
for j in range(0, i):
if dp[j] and s[j:i] in wordDict:
dp[i] = True
break
return dp[len(s)]
```