@@ -55,11 +55,11 @@
 | [Graph](https://.com/fluency03/leetcode-java/blob/master/src/graph) |
 
 
-# Total: 534
+# Total: 535
 
 | Easy | Medium | Hard | - |
 |:-------:|:-------:|:----:|:---:|
-| 142 | 290 | 90 | 12 |
+| 142 | 291 | 90 | 12 |
 
 
 | Question | Solution | Difficulty |
@@ -484,6 +484,13 @@
 | [646. Maximum Length of Pair Chain](https://leetcode.com/problems/maximum-length-of-pair-chain/) | [Solution](https://.com/fluency03/leetcode-java/blob/master/src/MaximumLengthOfPairChain646.java) | Medium |
 | [647. Palindromic Substrings](https://leetcode.com/problems/palindromic-substrings/) | [Solution](https://.com/fluency03/leetcode-java/blob/master/src/PalindromicSubstrings647.java) | Medium |
 | [648. Replace Words](https://leetcode.com/problems/replace-words/) | [Solution](https://.com/fluency03/leetcode-java/blob/master/src/ReplaceWords648.java) | Medium |
+
+
+
+| [652. Find Duplicate Subtrees](https://leetcode.com/problems/find-duplicate-subtrees/) | [Solution](https://.com/fluency03/leetcode-java/blob/master/src/FindDuplicateSubtrees652.java) | Medium |
+
+
+
 | [653. Two Sum IV - Input is a BST](https://leetcode.com/problems/two-sum-iv-input-is-a-bst/) | [Solution](https://.com/fluency03/leetcode-java/blob/master/src/TwoSumIVInputIsABST653.java) | Easy |
 | [654. Maximum Binary Tree](https://leetcode.com/problems/maximum-binary-tree/) | [Solution](https://.com/fluency03/leetcode-java/blob/master/src/MaximumBinaryTree654.java) | Medium |
 | [657. Judge Route Circle](https://leetcode.com/problems/judge-route-circle/) | [Solution](https://.com/fluency03/leetcode-java/blob/master/src/JudgeRouteCircle657.java) | Easy |

@@ -0,0 +1,68 @@
+/**
+* Given a binary tree, return all duplicate subtrees. For each kind of
+* duplicate subtrees, you only need to return the root node of any one of them.
+*
+* Two trees are duplicate if they have the same structure with same node values.
+*
+* Example 1:
+*
+* 1
+* / \
+* 2 3
+* / / \
+* 4 2 4
+* /
+* 4
+*
+* The following are two duplicate subtrees:
+*
+* 2
+* /
+* 4
+*
+* and
+*
+* 4
+*
+* Therefore, you need to return above trees' root in the form of a list.
+*/
+
+/**
+* Definition for a binary tree node.
+* public class TreeNode {
+* int val;
+* TreeNode left;
+* TreeNode right;
+* TreeNode(int x) { val = x; }
+* }
+*/
+
+public class FindDuplicateSubtrees652 {
+public List<TreeNode> findDuplicateSubtrees(TreeNode root) {
+List<TreeNode> res = new ArrayList<>();
+if (root == null) return res;
+Map<String, Boolean> visited = new HashMap<>();
+findDuplicates(root, visited, res);
+return res;
+}
+
+private String findDuplicates(TreeNode root, Map<String, Boolean> visited, List<TreeNode> res) {
+if (root == null) {
+return "N";
+}
+String self = Integer.toString(root.val);
+String left = findDuplicates(root.left, visited, res);
+String right = findDuplicates(root.right, visited, res);
+String curr = self + "-" + left + "-" + right;
+if (!visited.containsKey(curr)) {
+visited.put(curr, false);
+} else {
+if (!visited.get(curr)) {
+res.add(root);
+visited.put(curr, true);
+}
+}
+return curr;
+}
+
+}