arraylist从大到小排序_java基础算法之二叉树排序（递归）

一、二叉树介绍

在计算机科学中，二叉树是每个结点最多有两个子树的树结构。二叉树由各种节点组成，如下图所示：

每个节点都可以有左子节点，右子节点
每一个节点都有一个值

二叉树遍历：

二叉树的遍历分左序，中序，右序

左序即：中间的数遍历后放在左边
中序即：中间的数遍历后放在中间
右序即：中间的数遍历后放在右边

二叉树排序法的思路：

假设通过二叉树对如下10个随机数进行排序

67,7,30,73,10,0,78,81,10,74

第一步：插入数据，插入基本逻辑是，小、相同的放左边，大的放右边

1. 67 放在根节点

2. 7 比 67小，放在67的左节点

3. 30 比67 小，找到67的左节点7，30比7大，就放在7的右节点

4. 73 比67大，放在67得右节点

5. 10 比 67小，找到67的左节点7，10比7大，找到7的右节点30，10比30小，放在30的左节点。

...

9. 10比67小，找到67的左节点7，10比7大，找到7的右节点30，10比30小，找到30的左节点10，10和10一样大，放在左边

插入数据之后的结果如下图所示：

第二步：二叉树“中序遍历”，把这些已经排好序的数据，遍历成我们常用的List或者数组的形式。

如图二所见，我们排序淡然希望遍历后的结果是从小到大的，所以应该采用中序遍历

Java源代码如下：

在插入和遍历的过程中都用到了迭代的思想。

package

启动程序，控制台打印的数据，效果如下：

D:javajdkJDK8_64binjava.exe "-javaagent:D:javaidea201903config-pathclassIntelliJ IDEA 2019.3.3libidea_rt.jar=55936:D:javaidea201903config-pathclassIntelliJ IDEA 2019.3.3bin" -Dfile.encoding=UTF-8 -classpath 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avaUTIL-PackagesmavenBigDatacomsquareupokhttpokhttp2.7.5okhttp-2.7.5.jar;D:javaUTIL-PackagesmavenBigDatacomsquareupokiookio1.6.0okio-1.6.0.jar;D:javaUTIL-PackagesmavenBigDatacomgoogleinjectextensionsguice-servlet4.0guice-servlet-4.0.jar com.bigdata.hadoop.mapreduce.second.Node
数据插入二叉树并排序完成，接下来完成遍历输出：
[0, 7, 10, 10, 30, 67, 73, 74, 78, 81]Process finished with exit code 0