word break

 1class Solution:
 2    def wordBreak(self, s, words):
 3        ok = [True]
 4        for i in range(1, len(s)+1):
 5            w = False
 6            for j in range(i):
 7                substring = s[j:i]
 8                if ok[j] and substring in words:
 9                    w = True
10                    break
11            ok += w,
12        return ok[-1]