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.
Companies:
Uber, Amazon, Google, Microsoft
Related Topics:
Tree
Similar Questions:
- Serialize and Deserialize Binary Tree (Hard)
- Serialize and Deserialize BST (Medium)
- Construct String from Binary Tree (Easy)
// OJ: https://leetcode.com/problems/find-duplicate-subtrees/
// Author: github.com/lzl124631x
// Time: O(N^2) since string concatenation takes O(N) time on average
// Space: O(N^2) since string take O(N) space on average
// Ref: https://leetcode.com/problems/find-duplicate-subtrees/solution/
class Solution {
private:
unordered_map<string, int> treeToCnt;
vector<TreeNode*> ans;
string collect(TreeNode *node) {
if (!node) return "#";
string s = to_string(node->val) + "," + collect(node->left) + "," + collect(node->right);
if (treeToCnt[s] == 1) ans.push_back(node);
treeToCnt[s]++;
return s;
}
public:
vector<TreeNode*> findDuplicateSubtrees(TreeNode* root) {
collect(root);
return ans;
}
};