04 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; }
 * }
 */
import java.util.*;
public class Solution {
    static public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
        if(pre== null || in ==null)
            return null;
        if ( pre.length != in.length){
            System.out.println("前序遍历长度与中序遍历长度不同,输入错误");
        }
        TreeNode root = reConstructBinaryTree(pre,0,pre.length -1,in, 0,in.length -1);
        return root;
    }
    public static TreeNode reConstructBinaryTree(int [] pre,int startpre, int endpre,int [] in,int startin,int endin){
        if ( startpre > endpre || startin > endin)
            return null;
        TreeNode root = new TreeNode( pre[startpre]);
        for (int i = startin; i <= endin; i++){
            if(pre[startpre] == in[i]){
                root.left = reConstructBinaryTree(pre,startpre+1,startpre+i-startin,in, startin,i-1);
                root.right = reConstructBinaryTree(pre,startpre+i-startin +1,endpre,in, i+1,endin);
            }
        }
        return root;
    }
    public static void main(String [] args){
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入前序遍历序列的长度");
        int lengthpre = sc.nextInt();
        int [] pre = new int[lengthpre];
        System.out.println("请输入前序遍历序列");
        for (int i =0;i< lengthpre;i++){
            pre[i] = sc.nextInt();
        }
        System.out.println("请输入中序遍历序列的长度");
        int lengthin = sc.nextInt();
        int [] in = new int[lengthin];
        System.out.println("请输入中序遍历序列");
        for(int j = 0; j< lengthin;j++){
            pre[j] = sc.nextInt();
        }
        reConstructBinaryTree(pre,in);
    }
}