剑指Offer_重建二叉树_04

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。

package test;

import java.util.LinkedList;

public class Test
{
	public static void main(String[] args)
	{
		int[] preOrder = {1,2,4,8,9,5,3,6,7};//前序遍历数组
		int[] midOrder = {8,4,9,2,5,1,6,3,7};//后序遍历数组
		TreeNode biTree = reConstructBiTree(preOrder,midOrder);//重构二叉树
		levelOrder(biTree);//层次遍历输出重构后的二叉树
	}
	
	public static TreeNode reConstructBiTree(int[] preOrder, int[] midOrder)
	{
		TreeNode root = reBiTree(preOrder,0,preOrder.length-1, midOrder,0,midOrder.length-1);
		return root;
	}
	
	public static TreeNode reBiTree(int[] pre, int preL, int preR, int[] mid, int midL, int midR)
	{//已知由二叉树的前序遍历、中序遍历重构二叉树。
		if(preL > preR || midL > midR)
			return null;
		
		TreeNode now = new TreeNode(pre[preL]);
		for(int i = midL; i <= midR; i++)
		{
			if(mid[i] == pre[preL])
			{
				now.left = reBiTree(pre,preL+1,i-midL+preL, mid,midL,i-1);
				now.right = reBiTree(pre,i-midL+preL+1,preR, mid,i+1,midR);
			}
		}
		
		 return now;
	}
	
	public static void levelOrder(TreeNode biTree)
	{//层次遍历
		if(biTree == null)
			return;
		LinkedList<TreeNode> list = new LinkedList<TreeNode>();
		list.add(biTree);
		TreeNode now;
		while(!list.isEmpty())
		{
			now = list.poll();
			System.out.println(now.value);
			if(now.left != null)
				list.add(now.left);
			if(now.right != null)
				list.add(now.right);
		}
	}
}

class TreeNode//节点结构
{
	int value;
	TreeNode left;
	TreeNode right;
	
	TreeNode(int value)
	{
		this.value = value;
	}
}