重建二叉树

输入某二叉树的前序遍历和中序遍历的结果，请重建该二叉树。假设输入的前序遍历和中序遍历的结果中都不含重复的数字。

例如，给出

前序遍历 preorder = [3,9,20,15,7]
中序遍历 inorder = [9,3,15,20,7]

返回如下的二叉树：

    3
   / \
  9  20
    /  \
   15   7

限制：
0 <= 节点个数 <= 5000

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        if(preorder == null || inorder == null){
            return null;
        }

        return rebuildBinaryTree(preorder, 0, preorder.length - 1, inorder, 0, inorder.length - 1);
    }

    private TreeNode rebuildBinaryTree(int[] preorder, int startPre, int endPre, int[] inorder, int startIn, int endIn){
        if(startPre > endPre ||startIn > endPre){
            return null;
        }

        TreeNode root = new TreeNode(preorder[startPre]);
        for(int i = startIn; i <= endIn; i++){
            if(root.val == inorder[i]){
                root.left = rebuildBinaryTree(preorder, startPre + 1 , startPre + (i - startIn), inorder, startIn, i - 1);
                root.right = rebuildBinaryTree(preorder, startPre + (i - startIn) + 1, endPre, inorder, i + 1, endPre );
                break;
            }
        }
        return root;
    }
}