剑指offer之重建二叉树（java）

题目描述

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) {          if (pre== null ||in== null )              return null ;          return reConstruct(pre, 0 ,pre.length- 1 ,in, 0 ,in.length- 1 );                }            public TreeNode reConstruct( int [] pre, int prestart, int preend, int [] in, int instart, int inend){          if (prestart>preend||instart>inend)              return null ;          TreeNode root= new TreeNode(pre[prestart]);          for ( int i=instart;i<=inend;i++){              if (in[i]==pre[prestart]){                  root.left=reConstruct(pre,prestart+ 1 ,prestart+i-instart,in,instart,i- 1 );                  root.right=reConstruct(pre,prestart+i-instart+ 1 ,preend,in,i+ 1 ,inend);              }          }          return root;      } }