diff --git a/Week_04/id_9/LeetCode_211_9.java b/Week_04/id_9/LeetCode_211_9.java
new file mode 100644
index 00000000..b24a574a
--- /dev/null
+++ b/Week_04/id_9/LeetCode_211_9.java
@@ -0,0 +1,130 @@
+package com.github.lifelab.leetcode.problemset;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Objects;
+import java.util.regex.Pattern;
+
+/**
+ * 添加与搜索单词 - 数据结构设计 @see https://leetcode-cn.com/problems/add-and-search-word-data-structure-design/
+ *
+ * @author Weichao Li (liweichao0102@gmail.com)
+ * @since 2019-06-30
+ */
+public class Solution211 {
+
+    /**
+     * hash + cache 实现
+     */
+    public class WordDictionary1 {
+
+        private Map<String, String> wd;
+
+        private Map<String, Boolean> cache;
+
+        /**
+         * Initialize your data structure here.
+         */
+        public WordDictionary1() {
+            this.wd = new HashMap<>();
+            this.cache = new HashMap<>();
+        }
+
+        /**
+         * Adds a word into the data structure.
+         */
+        public void addWord(String word) {
+            wd.put(word, word);
+        }
+
+        /**
+         * Returns if the word is in the data structure. A word could contain the dot character '.' to represent any one letter.
+         */
+        public boolean search(String word) {
+            Boolean cacheValue = cache.get(word);
+            if (Objects.nonNull(cacheValue) && cacheValue) {
+                return cacheValue;
+            } else {
+                cacheValue = wd.keySet().parallelStream().anyMatch(e -> Pattern.matches(word, e));
+                cache.put(word, cacheValue);
+            }
+            return cacheValue;
+        }
+
+    }
+
+    /**
+     * tree 实现
+     */
+    public class WordDictionary2 {
+
+        class Node {
+
+            private Node[] next;
+
+            private boolean isWord;
+
+            public Node() {
+                next = new Node[26];
+                isWord = false;
+            }
+        }
+
+        private Node root;
+
+        /**
+         * Initialize your data structure here.
+         */
+        public WordDictionary2() {
+            root = new Node();
+        }
+
+        /**
+         * Adds a word into the data structure.
+         */
+        public void addWord(String word) {
+            int len = word.length();
+            Node curNode = root;
+            for (int i = 0; i < len; i++) {
+                char curChar = word.charAt(i);
+                Node next = curNode.next[curChar - 'a'];
+                if (next == null) {
+                    curNode.next[curChar - 'a'] = new Node();
+                }
+                curNode = curNode.next[curChar - 'a'];
+            }
+            if (!curNode.isWord) {
+                curNode.isWord = true;
+            }
+        }
+
+        /**
+         * Returns if the word is in the data structure. A word could contain the dot character '.' to represent any one letter.
+         */
+        public boolean search(String word) {
+            return match(word, root, 0);
+        }
+
+        private boolean match(String word, Node node, int start) {
+            if (start == word.length()) {
+                return node.isWord;
+            }
+            char alpha = word.charAt(start);
+            if (alpha == '.') {
+                for (int i = 0; i < 26; i++) {
+                    if (node.next[i] != null && match(word, node.next[i], start + 1)) {
+                        return true;
+                    }
+                }
+                return false;
+            } else {
+                if (node.next[alpha - 'a'] == null) {
+                    return false;
+
+                }
+                return match(word, node.next[alpha - 'a'], start + 1);
+            }
+        }
+    }
+
+}
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diff --git a/Week_04/id_9/LeetCode_78_9.java b/Week_04/id_9/LeetCode_78_9.java
new file mode 100644
index 00000000..09358f28
--- /dev/null
+++ b/Week_04/id_9/LeetCode_78_9.java
@@ -0,0 +1,38 @@
+package com.github.lifelab.leetcode.problemset;
+
+import java.util.LinkedList;
+import java.util.List;
+
+/**
+ * 子集 @see https://leetcode-cn.com/problems/subsets/
+ *
+ * @author Weichao Li (liweichao0102@gmail.com)
+ * @since 2019-06-30
+ */
+public class Solution78 {
+
+    public List<List<Integer>> subsets(int[] nums) {
+
+        List<List<Integer>> list = new LinkedList<>();
+        traverse(nums, 0, list, new LinkedList<>());
+        return list;
+
+    }
+
+    private void traverse(int[] nums, int index, List<List<Integer>> list, List<Integer> currentList) {
+
+        //terminal
+        if (nums.length == index) {
+            list.add(currentList);
+            return;
+        }
+        // process & drill down
+        List<Integer> target = new LinkedList<>(currentList);
+
+        target.add(nums[index]);
+
+        traverse(nums, index + 1, list, currentList);
+
+        traverse(nums, index + 1, list, target);
+    }
+}
\ No newline at end of file