Find Duplicate Subtrees LeetCode Solution

Problem – Find Duplicate Subtrees

Given the root of 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 the same node values.

Example 1:

Input: root = [1,2,3,4,null,2,4,null,null,4]
Output: [[2,4],[4]]

Example 2:

Input: root = [2,1,1]
Output: [[1]]

Example 3:

Input: root = [2,2,2,3,null,3,null]
Output: [[2,3],[3]]


  • The number of the nodes in the tree will be in the range [1, 10^4]
  • -200 <= Node.val <= 200

Find Duplicate Subtrees LeetCode Solution in C++

class Solution {
    vector<TreeNode*> findDuplicateSubtrees(TreeNode* root) {
        unordered_map<string, vector<TreeNode*>> map;
        vector<TreeNode*> dups;
        serialize(root, map);
        for (auto it = map.begin(); it != map.end(); it++)
            if (it->second.size() > 1) dups.push_back(it->second[0]);
        return dups;
    string serialize(TreeNode* node, unordered_map<string, vector<TreeNode*>>& map) {
        if (!node) return "";
        string s = "(" + serialize(node->left, map) + to_string(node->val) + serialize(node->right, map) + ")";
        return s;

Find Duplicate Subtrees LeetCode Solution in Java

class Solution {
    public List<TreeNode> findDuplicateSubtrees(TreeNode root) {
        Map<String, List<TreeNode>> map = new HashMap<String, List<TreeNode>>();
        List<TreeNode> dups = new ArrayList<TreeNode>();
        serialize(root, map);
        for (List<TreeNode> group : map.values())
            if (group.size() > 1) dups.add(group.get(0));
        return dups;

    private String serialize(TreeNode node, Map<String, List<TreeNode>> map) {
        if (node == null) return "";
        String s = "(" + serialize(node.left, map) + node.val + serialize(node.right, map) + ")";
        if (!map.containsKey(s)) map.put(s, new ArrayList<TreeNode>());
        return s;

Find Duplicate Subtrees LeetCode Solution in Python

def findDuplicateSubtrees(self, root):
        def trv(root):
            if not root: return "null"
            struct = "%s,%s,%s" % (str(root.val), trv(root.left), trv(root.right))
            return struct
        nodes = collections.defaultdict(list)
        return [nodes[struct][0] for struct in nodes if len(nodes[struct]) > 1]
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