Update 0105.Construct-Binary-Tree-from-Preorder-and-Inorder-Traversal.md

update a new answer for less memory cost.

website/content/ChapterFour/0100~0199/0105.Construct-Binary-Tree-from-Preorder-and-Inorder-Traversal.md

@@ -70,6 +70,21 @@ func buildPreIn2TreeDFS(pre []int, preStart int, preEnd int, inStart int, inPos
 	return root
 }
 
+// 解法 2, 直接传入需要的 slice 范围作为输入, 可以避免申请对应 inorder 索引的内存, 内存使用(leetcode test case) 4.7MB -> 4.3MB.
+func buildTree(preorder []int, inorder []int) *TreeNode {
+    if len(preorder) == 0 {
+        return nil
+    }
+    root := &TreeNode{Val:preorder[0]}
+    for pos, node := range inorder {
+        if node == root.Val {
+            root.Left  = buildTree(preorder[1:pos+1], inorder[:pos]) 
+            root.Right = buildTree(preorder[pos+1:], inorder[pos+1:])
+        }
+    }
+    return root
+}
+
 ```