Create 140. Word Break II.cpp

Author: ZengruiWang

140. Word Break II.cpp

@@ -0,0 +1,31 @@
+class Solution {
+public:
+    void dfs(int start, string &sentence, vector<string> &res, const string &s, const unordered_set<string> &dict, const vector<bool> &breakable){
+        if(start == s.length()) res.push_back(sentence.substr(0, sentence.size() - 1));
+        string substr, origin = sentence;
+        for(int i = start; i < s.length(); ++i){
+            substr = s.substr(start, i - start + 1);
+            if(dict.find(substr) != dict.end() && breakable[i + 1]){
+                sentence.append(substr).append(" ");
+                dfs(i + 1, sentence, res, s, dict, breakable);
+                sentence = origin;
+            }
+        }
+    }
+    vector<string> wordBreak(string s, unordered_set<string>& wordDict) {
+        const size_t n = s.length();
+        vector<string> res;
+        string sentence = "", substr;
+        vector<bool> breakable(n + 1, false);
+        breakable[n] = true;
+        for(int i = n - 1; i >= 0; --i){
+            for(int j = i; j < n; ++j){
+                substr = s.substr(i, j - i + 1);
+                if(breakable[j + 1] && wordDict.find(substr) != wordDict.end())
+                    breakable[i] = true;
+            }
+        }
+        dfs(0, sentence, res, s, wordDict, breakable);
+        return res;
+    }
+};