不使用递归遍历二叉树

不使用递归，想要遍历二叉树，只能通过循环来实现。不是所有的递归都能转化为循环，但这个遍历可以转换。使用循环遍历二叉树还必须使用栈进行回溯算法。下面给出示例代码：

import java.util.Stack;

public class AnswerB13 {

	public static void main(String[] args) {
		Node tree = makeupTree();
		Stack<Node> stack = new Stack<Node>();
		Node currentNode = tree;
		while (currentNode != null) {
			System.out.println(currentNode.value);
			stack.push(currentNode);
			currentNode = currentNode.left;
			if (currentNode == null) {
				Node parent = stack.pop();
				currentNode = parent.right;
				if (currentNode == null) {
					if (stack.isEmpty()) {
						break;
					}
					Node parentParent = stack.pop();
					currentNode = parentParent.right;
				}
			}
		}
	}

	private static Node makeupTree() {
		Node root = new Node(0);
		Node node1 = new Node(1);
		Node node2 = new Node(2);
		Node node11 = new Node(11);
		Node node12 = new Node(12);
		Node node21 = new Node(21);
		Node node22 = new Node(22);

		root.left = node1;
		root.right = node2;

		node1.left = node11;
		node1.right = node12;

		node2.left = node21;
		node2.right = node22;
		return root;
	}

	public static class Node {
		public Node left;
		public Node right;
		public int value;

		public Node(int value) {
			this.value = value;
		}
	}
}