剑指 Offer 07. 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

class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        int n = preorder.length;
        if (n == 0)
        {
            return null;
        }
        int rootVal = preorder[0], rootIndex = 0;
        for (int i = 0; i < n;i++)
        {
            if (inorder[i] == rootVal)
            {
                rootIndex = i;
                break;
            }
        }
        TreeNode root = new TreeNode(rootVal);
        root.left = buildTree(Arrays.copyOfRange(preorder,1,1+rootIndex),Arrays.copyOfRange(inorder,0,rootIndex));
        root.right = buildTree(Arrays.copyOfRange(preorder,1+rootIndex,n),Arrays.copyOfRange(inorder,rootIndex + 1, n));
        return root;
    }
}