diff --git a/Hard/SubstringwithConcatenationofAllWords.java b/Hard/SubstringwithConcatenationofAllWords.java
new file mode 100644
index 00000000..e1e70890
--- /dev/null
+++ b/Hard/SubstringwithConcatenationofAllWords.java
@@ -0,0 +1,80 @@
+import java.util.*;
+
+/**
+ * 30. Substring with Concatenation of All Words   
+ * You are given a string, s, and a list of words, words, that are all of the same length. Find all starting indices of substring(s) in s that is a concatenation of each word in words exactly once and without any intervening characters.
+ * For example, given:
+ * s: "barfoothefoobarman" words: ["foo", "bar"]  You should return the indices: [0,9].
+ * Tags: Hash Table Two Pointers String
+ * Similar Problems: (H) Minimum Window Substring
+ * @author chenshuna
+ */ 
+
+public class SubstringwithConcatenationofAllWords {
+    public static List<Integer> findSubstring(String s, String[] words) {
+        List<Integer> res = new ArrayList<Integer>();
+        if( s==null || words == null || s.length() == 0 || words.length == 0 ) return res;
+        HashMap<String, Integer> wordDict = new HashMap<String, Integer>();
+        int wordLen = words[0].length();
+        for(String word : words){
+            if(wordDict.containsKey(word))
+                wordDict.put(word, wordDict.get(word) + 1);
+            else 
+                wordDict.put(word, 1);
+        }
+        /**
+         * outside loop
+         *  bar/foo/the/foo/bar/man
+         *  b/arf/oot/hef/oob/arm/an
+         *  ba/rfo/oth/efo/oba/rma/n
+         */ 
+        for(int i = 0; i < wordLen; i++){
+            HashMap<String, Integer> sMap = new HashMap<String, Integer>();
+            int count = 0;
+            int start = i;
+            for(int j = i; j <= s.length() - wordLen; j = j + wordLen){
+                String temp = s.substring(j, j + wordLen);
+                if(wordDict.containsKey(temp)){
+                    if(sMap.containsKey(temp))
+                         sMap.put(temp, sMap.get(temp) + 1);
+                    else 
+                         sMap.put(temp, 1);
+                    
+                    if(sMap.get(temp) <= wordDict.get(temp))
+                        count++;
+                    else
+                    {
+                        while(sMap.get(temp) > wordDict.get(temp))
+                        {
+                            String temp2 = s.substring(start, start + wordLen);
+                            sMap.put(temp2, sMap.get(temp2) - 1);
+                            if(sMap.get(temp2) < wordDict.get(temp2)) count--;
+                            start = start + wordLen;
+                        }
+                    }
+                
+                    if(count == words.length){
+                        res.add(start);
+                        String word = s.substring(start, start + wordLen);
+                        sMap.put(word, sMap.get(word) - 1);
+                        count--;
+                        start = start + wordLen;
+                    }
+                }
+                else
+                {
+                    sMap.clear();
+                    count = 0;
+                    start = j + wordLen;
+                }
+            }
+        }
+        return res;
+    }
+
+    public static void main(String[] args) {
+        String s = "barfoothefoobarman";
+        String[] words = {"foo", "bar"};
+        System.out.println(findSubstring(s, words));
+    }
+}
\ No newline at end of file