二叉树先序中序后序

大家首先要明白想要得到先序中序后序遍历分为递归和非递归方法

递归非递归

递归方式比较好理解，直接上代码！

//先序遍历
public void f(Node head){
	if(head == null){
		return; 
	}
	System.out.println(head.val);
	f(head.left);
	f(head.right);
}
//中序遍历
public void f(Node head){
	if(head == null){
		return; 
	}
	f(head.left);
	System.out.println(head.val);
	f(head.right);
}
//后序遍历
public void f(Node head){
	if(head == null){
		return; 
	}
	f(head.left);
	f(head.right);
	System.out.println(head.val);
}

//先序遍历
public void f(Node head){
	Stack stack = new Stack();
	stack.push(head);
	while(!stack.isEmpty()){
		Node help = stack.pop();
		System.out.print(help.val + " ");
		if(help.right != null){
			stack.push(help.right); 
		}
		if(help.left != null){
			stack.push(help.left); 
		}
	}
	System.out.println();
}
//中序遍历
public void f(Node head){
	Stack stack1 = new Stack();
	Stack stack2 = new Stack();
	stack1.push(head);
	while(!stack1.isEmpty()){
		Node help = stack1.pop();
		Stack2.push(help);
		if(head.left != null){
			stack1.push(head.left); 
		} 
		if(head.right != null){
			stack1.push(head.rigth); 
		} 
	}
	while(!stack2.isEmpty()){
		System.out.print(stack2.pop().val + " "); 
	}
	System.out.println();
}

//后续遍历
public void f(Node head){
	if(head != null){
		Stack stack = new Stack();
		if(head != null){
			stack.push(head);
			head = head.left; 
		} else{
			head = stack.pop();
			System.out.print(head.val + " ");
			head = head.right; 
		}
	}
	System.out.println();
}