LeetCode in Kotlin
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, 5000] -200 <= Node.val <= 200
Solution
import com_github_leetcode.TreeNode
/*
* Example:
* var ti = TreeNode(5)
* var v = ti.`val`
* Definition for a binary tree node.
* class TreeNode(var `val`: Int) {
* var left: TreeNode? = null
* var right: TreeNode? = null
* }
*/
class Solution {
fun findDuplicateSubtrees(root: TreeNode?): List<TreeNode> {
val map: MutableMap<String, Int> = HashMap()
val list: MutableList<TreeNode> = ArrayList<TreeNode>()
helper(root, map, list)
return list
}
private fun helper(root: TreeNode?, map: MutableMap<String, Int>, list: MutableList<TreeNode>): String {
if (root == null) {
return "#"
}
val key = helper(root.left, map, list) + "#" + helper(root.right, map, list) + "#" + root.`val`
map[key] = map.getOrDefault(key, 0) + 1
if (map[key] == 2) {
list.add(root)
}
return key
}
}