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; }

 * }

 */

publicclassSolution {

    publicTreeNode reConstructBinaryTree(int[] pre,int[] in) {

        if(pre==null||in==null)

            returnnull;

        returnreConstruct(pre,0,pre.length-1,in,0,in.length-1);

         

    }

     

    publicTreeNode reConstruct(int[] pre,intprestart,intpreend,int[] in,intinstart,intinend){

        if(prestart>preend||instart>inend)

            returnnull;

        TreeNode root=newTreeNode(pre[prestart]);

        for(inti=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);

            }

        }

        returnroot;

    }

}