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
/**
* 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.length==0 || inorder.length==0){
return null;
}
TreeNode root=new TreeNode(preorder[0]);
for(int i=0;i<inorder.length;i++){
if(inorder[i]==preorder[0]){
root.left=buildTree(Arrays.copyOfRange(preorder,1,i+1),Arrays.copyOfRange(inorder,0,i));
root.right=buildTree(Arrays.copyOfRange(preorder,i+1,preorder.length),Arrays.copyOfRange(inorder,i+1,inorder.length));
break;
}
}
return root;
}
}
