给定一个非空字符串 s 和一个包含非空单词列表的字典 wordDict，在字符串中增加空格来构建一个句子，使得句子中所有的单词都在词典中。返回所有这些可能的句子。
说明：
- 分隔时可以重复使用字典中的单词。
- 你可以假设字典中没有重复的单词。
示例 1：
输入:
s = "catsanddog"
wordDict = ["cat", "cats", "and", "sand", "dog"]
输出:
[
"cats and dog",
"cat sand dog"
]
示例 2：
输入:
s = "pineapplepenapple"
wordDict = ["apple", "pen", "applepen", "pine", "pineapple"]
输出:
[
"pine apple pen apple",
"pineapple pen apple",
"pine applepen apple"
]
解释: 注意你可以重复使用字典中的单词。
示例 3：
输入:
s = "catsandog"
wordDict = ["cats", "dog", "sand", "and", "cat"]
输出:
[]
代码
class Solution {
public:
vector<string> wordBreak(string s, vector<string>& wordDict) {
unordered_map<string, vector<string>> m;
return helper(s, wordDict, m);
}
vector<string> helper(string s, vector<string>& wordDict, unordered_map<string, vector<string>>& m) {
if (m.count(s)) return m[s];
if (s.empty()) return {""};
vector<string> res;
for (string word : wordDict) {
if (s.substr(0, word.size()) != word) continue;
vector<string> rem = helper(s.substr(word.size()), wordDict, m);
for (string str : rem) {
res.push_back(word + (str.empty() ? "" : " ") + str);
}
}
return m[s] = res;
}
};
