遍历树, 前序 中序 后续

记录二叉树的遍历

public class PrintTree {

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

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

    }

    public static void main(String[] args) {
        Node node = new Node(7);
        node.left = new Node(3);
        node.right = new Node(6);

        node.left.left = new Node(1);
        node.left.right = new Node(2);

        node.right.left = new Node(4);
        node.right.right = new Node(5);


        // postorderForeach(node); // 123
        // inorderForeach(node);  // 213
        // preorderForeach(node);  // 7312
    }

    // 非递归, 实现遍历   <前序,  ^中序, >后续
    private static void postorderForeach(Node root) {
        Stack<Node> stack = new Stack<>();
        stack.push(root);

        Node lastNode = null;
        Node cur;
        while (!stack.isEmpty()) {
            cur = stack.peek();
            if (cur.left != null && cur.left != lastNode && cur.right != lastNode) {
                stack.push(cur.left);
                continue;
            }

            if (cur.right != null && cur.right != lastNode) {
                stack.push(cur.right);
                continue;
            }

            System.out.println(cur.value);
            lastNode = stack.pop();
        }


    }


    // 中序遍历
    private static void inorderForeach(Node root) {
        Stack<Node> stack = new Stack<>();
        Node cur = root;
        while (cur != null || !stack.isEmpty()) {

            if (cur != null) {
                stack.push(cur);
                // cur = cur.left;
                cur = cur.right;
                continue;
            }

            cur = stack.pop();
            System.out.println(cur.value);
            // cur = cur.right;
            cur = cur.left;
        }

    }

    // 前序遍历
    private static void preorderForeach(Node root) {
        Stack<Node> stack = new Stack<>();
        Node cur = root;
        while (cur != null || !stack.isEmpty()) {

            if (cur != null) {
                System.out.println(cur.value);
                stack.push(cur);
                cur = cur.left;
                continue;
            }

            cur = stack.pop();
            cur = cur.right;
        }
    }

}