Merge pull request #1964 from delight010/main

[SeongA] WEEK 15 solutions

Author: delight010

construct-binary-tree-from-preorder-and-inorder-traversal/delight010.swift

@@ -0,0 +1,28 @@
+class Solution {
+    // Time O(N^2)
+    // Space O(N)
+    func buildTree(_ preorder: [Int], _ inorder: [Int]) -> TreeNode? {
+        return buildTree(preorder[...], inorder[...])
+    }
+    
+    func buildTree(_ preorder: ArraySlice<Int>, _ inorder: ArraySlice<Int>) -> TreeNode? {
+        if preorder.isEmpty {
+            return nil
+        }
+        
+        let rootNode = TreeNode(preorder.first!)
+        var rootIndex = 0
+        
+        for (index, value) in inorder.enumerated() {
+            if value == rootNode.val {
+                rootIndex = index
+                break
+            }
+        }
+        rootNode.left = buildTree(preorder[preorder.startIndex + 1..<preorder.startIndex + rootIndex + 1], inorder[inorder.startIndex..<inorder.startIndex + rootIndex])
+        rootNode.right = buildTree(preorder[preorder.startIndex + 1 + rootIndex..<preorder.endIndex], inorder[inorder.startIndex + 1 + rootIndex..<inorder.endIndex])
+        
+        return rootNode
+    }
+}
+ 

subtree-of-another-tree/delight010.swift

@@ -0,0 +1,20 @@
+class Solution {
+    // Time O(M * N)
+    // Space O(M + N)
+    func isSubtree(_ root: TreeNode?, _ subRoot: TreeNode?) -> Bool {
+        if let root = root, let subRoot = subRoot {
+            return dfs(root, subRoot) || isSubtree(root.left, subRoot) || isSubtree(root.right, subRoot)
+        }
+        
+        return root == nil && subRoot == nil
+    }
+    
+    private func dfs(_ root: TreeNode?, subRoot: TreeNode?) -> Bool {
+        if let root = root, let subRoot = subRoot {
+            return root.val == subRoot.val && dfs(root.left, subRoot.left) && dfs(root.right, subRoot.right)
+        }
+        
+        return root == nil && subRoot == nil
+    }
+}
+