Construct Tree from given Inorder and Preorder traversals

Problem:
Give two strings representing the inorder and preorder traversals of binary tree, construct the tree.

The key here is that preorder traversal, the first char is the tree root. And then based on that char, find the its position in inorder string, then its left portion of in order string is the left subtree, right portion is the right subtree.

And do it recursively, make it simpler.

public static Node constructTree(String pre, String in){

if(pre.isEmpty())

return null;

if(pre.length() == 1)

return new Node(pre.charAt(0));

Node root = new Node(pre.charAt(0));

String[] ins = splitStringBy(in, pre.charAt(0));

                root.left = constructTree(pre.substring(1, ins[0].length()+1), ins[0]);

root.right = constructTree(pre.substring(ins[0].length()+1), ins[1]);

return root;

}

public static String[] splitStringBy(String str, char root){

String[] re = new String[2];

re[0] = str.substring(0, str.indexOf(root));

re[1] = str.substring(str.indexOf(root)+1);

return re;

}