复习数据结构

public class Test_01 {
    static class Node {
        Node parent;
        Node left;
        Node right;
        String content;
        boolean visited;
        Node(String content) {
            this.content = content;
        }

        void setLeft(Node left) {
            this.left = left;
            left.parent = this;
        }

        void setRight(Node right) {
            this.right = right;
            right.parent = this;
        }
    }

    public static void main(String[] args) {
        Node na = new Node("A");
        Node nb = new Node("B");
        Node nc = new Node("C");
        Node nd = new Node("D");
        Node ne = new Node("E");
        Node nf = new Node("F");
        Node ng = new Node("G");
        Node nh = new Node("H");
        Node ni = new Node("I");

        na.setLeft(nb);
        na.setRight(nc);

        nb.setLeft(nd);
        nb.setRight(ne);

        nc.setLeft(nf);
        nc.setRight(ng);

        ne.setLeft(ni);
        nf.setLeft(nh);

        test1(na);
        System.out.println();
        System.out.println("==========================");
        test2(na);
        System.out.println();
        System.out.println("==========================");
        test3(na);
        System.out.println();
        System.out.println("==========================");
        test4(na);
        System.out.println();
        System.out.println("==========================");
        test5(na);
        System.out.println();
        System.out.println("==========================");
        test6(na);
    }

    private static void test1(Node root) {
        if (root != null) {
            System.out.print(root.content+",");
            test1(root.left);
            test1(root.right);
        }
    }

    private static void test2(Node root) {
        if (root != null) {
            test2(root.left);
            System.out.print(root.content+",");
            test2(root.right);
        }
    }

    private static void test3(Node root) {
        if (root != null) {
            test3(root.left);
            test3(root.right);
            System.out.print(root.content+",");
        }
    }

    private static void test4(Node root) {
        Stack<Node> stack = new Stack<Node>();
        Node current = root;
        while (current != null || !stack.isEmpty()) {
            while (current != null) {
                stack.push(current);
                current = current.left;
            }
            current = stack.peek();
            stack.pop();
            System.out.print(current.content+",");
            current = current.right;
        }
    }

    private static void test5(Node root) {
        Stack<Node> stack = new Stack<Node>();
        Node current = root;
        while (current != null || !stack.isEmpty()) {
            while (current != null) {
                System.out.print(current.content+",");
                stack.push(current);
                current = current.left;
            }
            current = stack.peek();
            stack.pop();
            current = current.right;
        }
    }

    private static void test6(Node root) {
        Stack<Node> stack = new Stack<Node>();
        Node current = root;
        while (current != null || !stack.isEmpty()) {
            while (current != null) {
                stack.push(current);
                current = current.left;
            }
            current = stack.peek();
            stack.pop();
            if (!current.visited) {
                current.visited = true;
                stack.push(current);
                current = current.right;
            } else {
                System.out.print(current.content+",");
                current = null;
            }
        }
    }
}