652. Find Duplicate Subtrees

Author: partho-maple

README.md

@@ -470,6 +470,7 @@ Check this [golden](https://tinyurl.com/ujopecz) post.
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 |43| [536. Construct Binary Tree from String](https://tinyurl.com/yyl5vuh7) | [Python](https://tinyurl.com/wu6rdaw/536_Construct_Binary_Tree_from_String.py), [Swift](https://tinyurl.com/wuja3c4/536_Construct_Binary_Tree_from_String.swift) | -- | Medium | -- |
+|44| [652. Find Duplicate Subtrees](https://tinyurl.com/y5zt6392) | [Python](https://tinyurl.com/wu6rdaw/652_Find_Duplicate_Subtrees.py), [Swift](https://tinyurl.com/wuja3c4/652_Find_Duplicate_Subtrees.swift) | -- | Medium | -- |
 
 </p>
 </details>

leetcode.com/swift/DS_ALGO_PRAC.playground/Sources/swift/652_Find_Duplicate_Subtrees.swift

@@ -0,0 +1,49 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     public var val: Int
+ *     public var left: TreeNode?
+ *     public var right: TreeNode?
+ *     public init() { self.val = 0; self.left = nil; self.right = nil; }
+ *     public init(_ val: Int) { self.val = val; self.left = nil; self.right = nil; }
+ *     public init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
+ *         self.val = val
+ *         self.left = left
+ *         self.right = right
+ *     }
+ * }
+ */
+import Foundation
+
+class Solution {
+    func findDuplicateSubtrees(_ root: TreeNode?) -> [TreeNode?] {
+        guard let root = root else {
+            return []
+        }
+        
+        var counter = [[String]:Int]()
+        var duplicates = [TreeNode]()
+        
+        nodeCountDFS(root, &counter, &duplicates)
+
+        return duplicates
+    }
+    
+    func nodeCountDFS(_ root: TreeNode?, _ counter: inout [[String]:Int], _ duplicates: inout [TreeNode]) -> [String] {
+        guard let root = root else {
+            return ["#"]
+        }
+
+        var inorder = [String]()
+        let left = nodeCountDFS(root.left, &counter, &duplicates)
+        let right = nodeCountDFS(root.right, &counter, &duplicates)
+        inorder = left + [String(root.val)] + right
+        counter[inorder, default: 0] += 1
+        
+        if counter[inorder] == 2 {
+            duplicates.append(root)
+        }
+        
+        return inorder
+    }
+}