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思路

用递归来连接

代码

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */class Solution {
           //将指定数组的指定范围复制到新数组中。    public TreeNode buildTree(int[] preorder, int[] inorder)    {
           if (preorder.length == 0 || inorder.length == 0)        {
               return null;        }        int n = preorder.length;        int rootVal = preorder[0], rootIndex = 0;        //遍历数组        for (int i = 0; i < n; i++)        {
               if (inorder[i] == rootVal)            {
                   rootIndex = i;                break;            }        }        TreeNode root = new TreeNode(rootVal);   //定义根结点        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;    }}

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