Given a non-empty string s and a dictionary wordDict containing a list of non-empty words, add spaces in s to construct a sentence where each word is a valid dictionary word. You may assume the dictionary does not contain duplicate words.
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"].
Solution：Backtracking + dp
思路：
Time Complexity: O(num_word * s.length) Space Complexity: O()
Solution Code：
class Solution {
public List<String> wordBreak(String s, List<String> wordList) {
Set<String> wordDict = new HashSet<>();
for(String word: wordList) wordDict.add(word);
return DFS(s, wordDict, new HashMap<String, LinkedList<String>>());
}
// DFS function returns an array including all substrings derived from s.
List<String> DFS(String s, Set<String> wordDict, HashMap<String, LinkedList<String>> map) {
if (map.containsKey(s))
return map.get(s);
LinkedList<String>res = new LinkedList<String>();
if (s.length() == 0) {
res.add("");
return res;
}
for (String word : wordDict) {
if (s.startsWith(word)) {
List<String>sublist = DFS(s.substring(word.length()), wordDict, map);
for (String sub : sublist)
res.add(word + (sub.isEmpty() ? "" : " ") + sub);
}
}
map.put(s, res);
return res;
}
}
