140. Word Break II

Given a string s and a dictionary of words dict, add spaces in s to construct a sentence where each word is a valid dictionary word.
Return all such possible sentences.
For example,

 given*s* = "catsanddog",
 *dict* = ["cat", "cats", "and", "sand", "dog"].
 A solution is ["cats and dog", "cat sand dog"].

第一步建立字符串中分词的状态，设 f[i] 为 boolean 状态表示以 s[0,i]能被
dict 分割，状态方程：
f�[i�][j] = true if s[i][j] ∈ ���dict

	c	a	t	s	a	n	d	d	o	g
c	F	F	T	T	F	F	F	F	F	F
a		F	F	F	F	F	F	F	F	F
t			F	F	F	F	F	F	F	F
s				F	F	F	T	F	F	F
a					F	F	T	F	F	F
n						F	F	F	F	F
d							F	F	F	F
d								F	F	T
o									F	F
g										F

第二部通过 DFS 恢复成句子。