剑指Offer第七题(Java实现)

题目：输入某二叉树的前序遍历和中序遍历结果，请重建该二叉树。假设输入的前序和中序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}，则重建二叉树并输出他的头结点。二叉树结点的定义如下
struct BinaryTreeNode
{
int m_nValue;
BinaryTreeNode* m_pLetf;
BinaryTreeNode* m_Rigth;
};

二叉树的结点类
package Ds;

public class BinaryNode {
public T data;
public BinaryNode left,right;

 public BinaryNode(T data,BinaryNodeleft,BinaryNoderight){
     this.data=data;
     this.left=left;
     this.right=right;
 }

 public BinaryNode(){

 }

 public BinaryNode(T data){
     this(data, null, null);
 }

 public String toString(){
     return this.data.toString();
 }

 public boolean isLeaf(){
     return this.left==null&&this.right==null;
 }

}

实现代码：

import java.util.Scanner;

import Ds.BinaryNode;
public class Test_07 {
       public static void main(String args[]) throws Exception{
              Scanner scan=new Scanner(System.in);
              System.out.print("请输入前序序列:");
              String preStr=scan.nextLine();
              System.out.print("请输入中序序列:");
              String inStr=scan.nextLine();

              String[] preOrder=preStr.split(",");
              String[] inOrder=inStr.split(",");
              int preLength=preOrder.length;
              int inLength=inOrder.length;

              BinaryNoderoot=construct(preOrder,inOrder,preLength,inLength);


              if(root!=null) 
               { 
                  System.out.print("前序序列为:");
                   preOrderTraverse(root);
               }
              else 
                  System.out.println("The tree is empty");

            if(root!=null) 
               { 
                  System.out.print("中序序列为:");
                   inOrderTraverse(root);
               }
              else 
                  System.out.println("The tree is empty");

           if(root!=null) 
               { 
                  System.out.print("后序序列为:");
                   postOrderTraverse(root);
               }
              else 
                  System.out.println("The tree is empty");

       }
  public static BinaryNode construct(String[] preorder,String[] inorder,int preLength,int inLength) throws Exception{
           if(preorder==null||inorder==null||preLength<=0||inLength<=0||preLength!=inLength)
               return null;
          return contructCore(preorder,0,preLength-1,inorder,0,inLength-1);
       }

public static BinaryNode contructCore(String[] preorder, int startPreorder,int endPreorder, String[] inorder, int startInorder,int endInorder) throws Exception {
               String rootValue=preorder[startPreorder];
               BinaryNoderoot=new BinaryNode();
               root.data=rootValue;
               root.left=null;
               root.right=null;

               if(startPreorder==endPreorder){
                   if(startInorder==endInorder&&preorder[startPreorder].equals(inorder[startInorder])){
                       return root;
                   }else
                       throw new Exception("Invalid input");
               }   

               int rootInorder=startInorder;

               while(rootInorder<=endInorder&&!inorder[rootInorder].equals(rootValue))
                     ++rootInorder;




           if(rootInorder==endInorder&&!inorder[rootInorder].equals(rootValue))
                 throw new Exception("Invalid input");


            int leftLength=rootInorder-startInorder;
            int leftPreorderEnd=startPreorder+leftLength;

            if(leftLength>0){
                  root.left=contructCore(preorder,startPreorder+1,leftPreorderEnd,inorder,startInorder,rootInorder-1);
            }
                if(leftLength1,endPreorder,inorder,rootInorder+1,endInorder);
            }

                return root;
    }

    //先序递归
       public static void preOrderTraverse(BinaryNode p){
             if(p!=null){
                 System.out.print(p.data.toString()+" ");
                 preOrderTraverse(p.left);
                 preOrderTraverse(p.right);
             }
       }


     //中序递归
       public static void inOrderTraverse(BinaryNodep){

           if(p!=null){
                 inOrderTraverse(p.left);
                 System.out.print(p.data.toString()+" ");
                 inOrderTraverse(p.right);
           }

       }

     //后序递归
          public static void postOrderTraverse(BinaryNodep){
              if(p!=null){
                  postOrderTraverse(p.left);
                  postOrderTraverse(p.right);
                  System.out.print(p.data.toString()+" ");
              }
          }



}  

运行结果：