[Tree] Refactor time and space complexity to two questions

Author: soapyigu

README.md

@@ -191,8 +191,8 @@
 [Binary Tree Vertical Order Traversal](https://leetcode.com/problems/binary-tree-vertical-order-traversal/)| [Swift](./Tree/BinaryTreeVerticalOrderTraversal.swift)| Medium| O(n)| O(n)|
 [Kth Smallest Element in a BST](https://leetcode.com/problems/kth-smallest-element-in-a-bst/)| [Swift](./Tree/KthSmallestElementBST.swift)| Medium| O(n)| O(n)|
 [Binary Tree Right Side View](https://leetcode.com/problems/binary-tree-right-side-view/)| [Swift](./Tree/BinaryTreeRightSideView.swift)| Medium| O(n)| O(n)|
-[Construct Binary Tree from Preorder and Inorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/)| [Swift](./Tree/ConstructBinaryTreePreorderInorder.swift)| Medium| O(n)| O(n)|
-[Construct Binary Tree from Inorder and Postorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/)| [Swift](./Tree/ConstructBinaryTreeInorderPostorder.swift)| Medium| O(n)| O(n)|
+[Construct Binary Tree from Preorder and Inorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/)| [Swift](./Tree/ConstructBinaryTreePreorderInorder.swift)| Medium| O(nlogn)| O(1)|
+[Construct Binary Tree from Inorder and Postorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/)| [Swift](./Tree/ConstructBinaryTreeInorderPostorder.swift)| Medium| O(nlogn)| O(1)|
 [Path Sum](https://leetcode.com/problems/path-sum/)| [Swift](./Tree/PathSum.swift)| Easy| O(n)| O(n)|
 [Path Sum II](https://leetcode.com/problems/path-sum-ii/)| [Swift](./Tree/PathSumII.swift)| Medium| O(n)| O(n)|
 [Path Sum III](https://leetcode.com/problems/path-sum-iii/)| [Swift](./Tree/PathSumIII.swift)| Easy| O(n^2)| O(1)|

Tree/ConstructBinaryTreeInorderPostorder.swift

@@ -2,7 +2,7 @@
  * Question Link: https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/
  * Primary idea: Always use the last element in postorder as root, 
  *               then find that one in inorder to get left and right subtrees
- * Time Complexity: O(n), Space Complexity: O(n)
+ * Time Complexity: O(nlogn), Space Complexity: O(1)
  * 
  * Definition for a binary tree node.
  * public class TreeNode {