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Hard/WordBreakII.java

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+import java.util.*;
+
+/**
+ * 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"].
+ * Tags:  Dynamic Programming Backtracking
+ * @author chenshuna
+ */ 
+
+public class WordBreakII {
+    static HashMap<Integer, List<String>> map = new HashMap<>();
+
+    public static List<String> wordBreak(String s, Set<String> wordDict) {
+        int maxLengthOfWordDict = 0;
+        for(String str : wordDict)
+            maxLengthOfWordDict = Math.max(maxLengthOfWordDict, str.length());
+        return helper(s, wordDict, 0, maxLengthOfWordDict);
+    }
+
+    public static List<String> helper(String s, Set<String> wordDict, int start, int max){
+        List<String> res = new ArrayList<>();
+        if(start == s.length()) {
+            res.add("");
+            return res;
+        }
+        for(int i = start + 1 ; i <= max + start && i <= s.length(); i++){
+            String temp  = s.substring(start, i);
+            if(wordDict.contains(temp)){
+                List<String> l;
+                if(map.containsKey(i))
+                    l = map.get(i);
+                else
+                    l = helper(s, wordDict, i, max);
+                for(String ss : l)
+                    res.add(temp + (ss.equals("") ? "" : " ") + ss);
+            }
+        }
+        map.put(start, res);
+        return res;
+    }
+
+    public static void main(String[] args) {
+        Set<String> wordDict = new HashSet<String>();
+        wordDict.add("cat");
+        wordDict.add("cats");
+        wordDict.add("and");
+        wordDict.add("sand");
+        wordDict.add("dog");
+        String s = "catsanddog";
+        System.out.print(wordBreak(s, wordDict));
+    }
+}