题解 | #重建二叉树#

参考的一个大佬的思想，真的太清晰了

import java.util.Arrays;
/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
        if (pre.length == 0 || in.length == 0) {//特殊情况特殊讨论
            return null;
        }
        TreeNode root = new TreeNode(pre[0]);//确定根节点
        int index=getRootindex(pre,in);
        root.left = reConstructBinaryTree(Arrays.copyOfRange(pre,1,index+1),Arrays.copyOfRange(in,0,index));
        root.right = reConstructBinaryTree(Arrays.copyOfRange(pre,index+1,pre.length),Arrays.copyOfRange(in,index+1,in.length));
        return root;
    }
    public int getRootindex(int[] pre,int[] mid){
        for(int i=0;i<mid.length;i++){
            if(mid[i]==pre[0]){
                return i;
            }
        }
        return 0;
    }
}