二叉树的遍历

1.二叉树的前序

package test;
//前序遍历的递归实现与非递归实现
import java.util.Stack;
public class Test 
{
	public static void main(String[] args)
	{
		TreeNode[] node = new TreeNode[10];//以数组形式生成一棵完全二叉树
		for(int i = 0; i < 10; i++)
		{
			node[i] = new TreeNode(i);
		}
		for(int i = 0; i < 10; i++)
		{
			if(i*2+1 < 10)
				node[i].left = node[i*2+1];
			if(i*2+2 < 10)
				node[i].right = node[i*2+2];
		}
		
		preOrderRe(node[0]);
	}
	
	public static void preOrderRe(TreeNode biTree)
	{//递归实现
		System.out.println(biTree.value);
		TreeNode leftTree = biTree.left;
		if(leftTree != null)
		{
			preOrderRe(leftTree);
		}
		TreeNode rightTree = biTree.right;
		if(rightTree != null)
		{
			preOrderRe(rightTree);
		}
	}
	
	public static void preOrder(TreeNode biTree)
	{//非递归实现
		Stack stack = new Stack();
		while(biTree != null || !stack.isEmpty())
		{
			while(biTree != null)
			{
				System.out.println(biTree.value);
				stack.push(biTree);
				biTree = biTree.left;
			}
			if(!stack.isEmpty())
			{
				biTree = stack.pop();
				biTree = biTree.right;
			}
		}
	}
}
 
class TreeNode//节点结构
{
	int value;
	TreeNode left;
	TreeNode right;
	
	TreeNode(int value)
	{
		this.value = value;
	}
}

2.二叉树的中序

import java.util.Stack;
public class Test 
{
	public static void main(String[] args)
	{
		TreeNode[] node = new TreeNode[10];//以数组形式生成一棵完全二叉树
		for(int i = 0; i < 10; i++)
		{
			node[i] = new TreeNode(i);
		}
		for(int i = 0; i < 10; i++)
		{
			if(i*2+1 < 10)
				node[i].left = node[i*2+1];
			if(i*2+2 < 10)
				node[i].right = node[i*2+2];
		}
		
		midOrderRe(node[0]);
		System.out.println();
		midOrder(node[0]);
	}
	
	public static void midOrderRe(TreeNode biTree)
	{//中序遍历递归实现
		if(biTree == null)
			return;
		else
		{
			midOrderRe(biTree.left);
			System.out.println(biTree.value);
			midOrderRe(biTree.right);
		}
	}
	
	
	public static void midOrder(TreeNode biTree)
	{//中序遍历费递归实现
		Stack stack = new Stack();
		while(biTree != null || !stack.isEmpty())
		{
			while(biTree != null)
			{
				stack.push(biTree);
				biTree = biTree.left;
			}
			if(!stack.isEmpty())
			{
				biTree = stack.pop();
				System.out.println(biTree.value);
				biTree = biTree.right;
			}
		}
	}
}
 
class TreeNode//节点结构
{
	int value;
	TreeNode left;
	TreeNode right;
	
	TreeNode(int value)
	{
		this.value = value;
	}
}

3.二叉树的后序

import java.util.Stack;
public class Test 
{
	public static void main(String[] args)
	{
		TreeNode[] node = new TreeNode[10];//以数组形式生成一棵完全二叉树
		for(int i = 0; i < 10; i++)
		{
			node[i] = new TreeNode(i);
		}
		for(int i = 0; i < 10; i++)
		{
			if(i*2+1 < 10)
				node[i].left = node[i*2+1];
			if(i*2+2 < 10)
				node[i].right = node[i*2+2];
		}
		
		postOrderRe(node[0]);
		System.out.println("***");
		postOrder(node[0]);
	}
	
	
	
	public static void postOrderRe(TreeNode biTree)
	{//后序遍历递归实现
		if(biTree == null)
			return;
		else
		{
			postOrderRe(biTree.left);
			postOrderRe(biTree.right);
			System.out.println(biTree.value);
		}
	}
	
	public static void postOrder(TreeNode biTree)
	{//后序遍历非递归实现
		int left = 1;//在辅助栈里表示左节点
		int right = 2;//在辅助栈里表示右节点
		Stack stack = new Stack();
		Stack stack2 = new Stack();//辅助栈，用来判断子节点返回父节点时处于左节点还是右节点。
		
		while(biTree != null || !stack.empty())
		{
			while(biTree != null)
			{//将节点压入栈1，并在栈2将节点标记为左节点
				stack.push(biTree);
				stack2.push(left);
				biTree = biTree.left;
			}
			
			while(!stack.empty() && stack2.peek() == right)
			{//如果是从右子节点返回父节点，则任务完成，将两个栈的栈顶弹出
				stack2.pop();
				System.out.println(stack.pop().value);
			}
			
			if(!stack.empty() && stack2.peek() == left)
			{//如果是从左子节点返回父节点，则将标记改为右子节点
				stack2.pop();
				stack2.push(right);
				biTree = stack.peek().right;
			}
				
		}
	}
}
 
class TreeNode//节点结构
{
	int value;
	TreeNode left;
	TreeNode right;
	
	TreeNode(int value)
	{
		this.value = value;
	}
}