思路

将中序数组按照下标i划分两部分，左子树的前序下标为1,...,i，右子树前序下标为i+1,...,length-1。

代码

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
import java.util.Arrays;
public class Solution {
    public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
        if(pre.length == 0 || in.length == 0)    return null;
        TreeNode root = new TreeNode(pre[0]);
        for(int i = 0; i < in.length; i++) {
            if(in[i] == pre[0]) {
                root.left = reConstructBinaryTree(Arrays.copyOfRange(pre,1,i+1), Arrays.copyOfRange(in,0,i));
                root.right = reConstructBinaryTree(Arrays.copyOfRange(pre,i+1,pre.length), Arrays.copyOfRange(in,i+1,in.length));
                break;
            }
        }
        return root;
    }
}

笔记

copyOfRange函数参数取值左闭右开。