/**

  * Definition for a binary tree node.

  * public class TreeNode {

  *     int val;

  *     TreeNode left;

  *     TreeNode right;

  *     TreeNode(int x) { val = x; }

  * }

  */

 public class Solution {

     public TreeNode buildTree(int[] preorder, int[] inorder) {

         if(preorder.length==0 || inorder.length==0) return null;

         TreeNode root = new TreeNode(preorder[0]);

         int i;

         for(i=0; i<inorder.length; i++){    //找到根节点在中序序列中的位置

             if(inorder[i] == preorder[0]) break;

         }

         int[] left, right, npreorder;

         if(i>0){

             left = new int[i];              //左子树中的节点

             System.arraycopy(inorder, 0, left, 0, left.length);

         }else left = new int[0];

         if(inorder.length - i -1 > 0){      //右子树中的节点

             right = new int[inorder.length - i -1];

             System.arraycopy(inorder, i+1, right, 0, right.length);

         }else right = new int[0];

         npreorder = new int[preorder.length - 1];//删除根节点

         System.arraycopy(preorder, 1, npreorder, 0, npreorder.length);

         root.left = buildTree(npreorder, left);  //构建左子树

         npreorder = new int[preorder.length - left.length - 1];//删除左子树中节点

         System.arraycopy(preorder, 1 + left.length, npreorder, 0, npreorder.length);

         root.right = buildTree(npreorder, right);//构建右子树

         return root;

     }

 }