LeetCode-in-Java
652. Find Duplicate Subtrees
Medium
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]]
Constraints:
- The number of the nodes in the tree will be in the range
[1, 10^4] -200 <= Node.val <= 200
Solution
import com_github_leetcode.TreeNode;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/*
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
public class Solution {
public List<TreeNode> findDuplicateSubtrees(TreeNode root) {
Map<String, Integer> map = new HashMap<>();
List<TreeNode> list = new ArrayList<>();
helper(root, map, list);
return list;
}
private String helper(TreeNode root, Map<String, Integer> map, List<TreeNode> list) {
if (root == null) {
return "#";
}
String key =
helper(root.left, map, list) + "#" + helper(root.right, map, list) + "#" + root.val;
map.put(key, map.getOrDefault(key, 0) + 1);
if (map.get(key) == 2) {
list.add(root);
}
return key;
}
}