牛客网 | 重建二叉树

输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。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。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并返回。

/** * 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) {        TreeNode head = constructBinaryTree(pre,0,pre.length-1,in,0,in.length-1);        return head;    }    public TreeNode constructBinaryTree(int [] pre, int preStart,int preEnd, int[] in,int inStart,int inEnd)    {        if(preStart>preEnd||inStart>inEnd) return null;        TreeNode newNode = new TreeNode(pre[preStart]);        for (int i=inStart;i<=inEnd;i++)        {            if(pre[preStart]==in[i])            {                newNode.left = constructBinaryTree(pre,preStart+1,preStart+i-inStart,in,inStart,i-1);                newNode.right = constructBinaryTree(pre,preStart+i-inStart+1,preEnd,in,i+1,inEnd);                break;            }        }        return newNode;    }}