二叉树非递归遍历 java

1、定义遍历用到的栈

public class Stack {

	static List list = new ArrayList();

	/**
	 * 判读栈是否为空
	 * 
	 * @return
	 */
	public static boolean isEmpty() {
		return list.isEmpty();
	}

	/**
	 * 出栈
	 * 
	 */
	public static TreeNode pull() {
		TreeNode node = list.get(list.size() - 1);
		list.remove(list.size() - 1);
		return node;
	}

	/**
	 * 出入栈
	 * 
	 * @param node
	 */
	public static void push(TreeNode node) {
		list.add(node);
	}

}

2、定义层次遍历用到的队列

public class Queue {
	static List list = new ArrayList();

	/**
	 * 入队
	 * 
	 * @param node
	 */
	public static void in(TreeNode node) {
		list.add(node);
	}

	/**
	 * 出队
	 */
	public static TreeNode out() {
		TreeNode tem = list.get(0);
		list.remove(0);
		return tem;
	}

	/**
	 * 判读队列是否为空
	 * 
	 * @return
	 */
	public static boolean isEmpty() {
		return list.isEmpty();
	}
}

3、遍历

       		H
	       / \
	      D   G
	     / \   \
	    B  C    F
	    \      /
	     A	   E

/*
 * 非递归遍历
 * @author Administrator
 *
 */
public class NoOrder {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		TreeNode root = init();
		System.out.println("非递归先序遍历");
		NoProOrder(root);
		System.out.println("非递归中序遍历");
		NoInOrder(root);
		System.out.println("层次遍历");
		levelOrder(root);
		/*System.out.println("非递归后序遍历");//写的不太对怎么
		NoPostOrder(root);*/

	}

	/** 构造树 */
	public static TreeNode init() {
		TreeNode a = new TreeNode('A');
		TreeNode b = new TreeNode('B', null, a);
		TreeNode c = new TreeNode('C');
		TreeNode d = new TreeNode('D', b, c);
		TreeNode e = new TreeNode('E');
		TreeNode f = new TreeNode('F', e, null);
		TreeNode g = new TreeNode('G', null, f);
		TreeNode h = new TreeNode('H', d, g);
		return h;// root
	}

	/**
	 * 非递归先序遍历
	 * 
	 * @param node
	 */
	public static void NoProOrder(TreeNode node) {
		// 创建队列
		Stack stack = new Stack();
		while (!stack.isEmpty() || node != null) {// 当栈不为空
			while (node != null) {
				System.out.println(node.value);
				stack.push(node);
				node = node.left;
			}
			if (!stack.isEmpty()) {
				node = stack.pull();
				node = node.right;
			}
		}
	}

	public static void NoInOrder(TreeNode node) {
		// 创建队列
		Stack stack = new Stack();
		while (!stack.isEmpty() || node != null) {// 当栈不为空
			while (node != null) {
				stack.push(node);
				node = node.left;
			}
			if (!stack.isEmpty()) {
				node = stack.pull();
				System.out.println(node.value);
				node = node.right;
			}
		}
	}

	/**
	 * 后续遍历，后续遍历的过程比稍微复杂一些，需要用到两个栈来实现
	 * 
	 * @param node
	 */
	public static void NoPostOrder(TreeNode node) {
		// 创建队列
		Stack stack1 = new Stack();
		Stack stack2 = new Stack();
		stack1.push(node);
		while (!stack1.isEmpty()) {
			node = stack1.pull();
			stack2.push(node);
			// 有左孩子就先压入左孩子
			if (node.left != null)
				stack1.push(node.left);
			// 有右孩子就后压入右孩子
			if (node.right != null)
				stack1.push(node.right);
		}
		// 逆序打印 根 -> 右 -> 左 的结果，就是后序遍历的结果
		while (!stack2.isEmpty())
			System.out.print(stack2.pull().value + " ");
	}

	/**
	 * 层次遍历
	 * 
	 * @param node
	 */
	public static void levelOrder(TreeNode node) {
		Queue queue = new Queue();
		while (!queue.isEmpty() || node != null) {
			if (node != null) {
				System.out.println(node.value);
				queue.in(node.left);
				queue.in(node.right);
			}
			node = queue.out();

		}
	}

}