solve problem

Author: delight010

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

@@ -0,0 +1,26 @@
+class Solution {
+    // Time O(N)
+    // Space O(N)
+    func buildTree(_ preorder: [Int], _ inorder: [Int]) -> TreeNode? {
+        if preorder.isEmpty {
+            return nil
+        }
+        
+        let totalCount = preorder.count
+        let rootNode = TreeNode(preorder[0])
+        var rootIndex = 0
+        
+        for (index, value) in inorder.enumerated() {
+            if value == rootNode.val {
+                rootIndex = index
+                break
+            }
+        }
+        
+        rootNode.left = buildTree(Array(preorder[1..<rootIndex + 1]), Array(inorder[0..<rootIndex + 1]))
+        rootNode.right = buildTree(Array(preorder[1 + rootIndex..<totalCount]), Array(inorder[1 + rootIndex..<totalCount]))
+        
+        return rootNode
+    }
+}
+