打印二叉树 递归和非递归

package chapter_3_binarytreeproblem;

import java.util.Stack;

public class Problem_01_PreInPosTraversal {

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

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

public static void preOrderRecur(Node head) {
    if (head == null) {
        return;
    }
    System.out.print(head.value + " ");
    preOrderRecur(head.left);
    preOrderRecur(head.right);
}

public static void inOrderRecur(Node head) {
    if (head == null) {
        return;
    }
    inOrderRecur(head.left);
    System.out.print(head.value + " ");
    inOrderRecur(head.right);
}

public static void posOrderRecur(Node head) {
    if (head == null) {
        return;
    }
    posOrderRecur(head.left);
    posOrderRecur(head.right);
    System.out.print(head.value + " ");
}

public static void preOrderUnRecur(Node head) {
    System.out.print("pre-order: ");
    if (head != null) {
        Stack<Node> stack = new Stack<Node>();
        stack.add(head);
        while (!stack.isEmpty()) {
            head = stack.pop();
            System.out.print(head.value + " ");
            if (head.right != null) {
                stack.push(head.right);
            }
            if (head.left != null) {
                stack.push(head.left);
            }
        }
    }
    System.out.println();
}

public static void inOrderUnRecur(Node head) {
    System.out.print("in-order: ");
    if (head != null) {
        Stack<Node> stack = new Stack<Node>();
        while (!stack.isEmpty() || head != null) {
            if (head != null) {
                stack.push(head);
                head = head.left;
            } else {
                head = stack.pop();
                System.out.print(head.value + " ");
                head = head.right;
            }
        }
    }
    System.out.println();
}

public static void posOrderUnRecur1(Node head) {
    System.out.print("pos-order: ");
    if (head != null) {
        Stack<Node> s1 = new Stack<Node>();
        Stack<Node> s2 = new Stack<Node>();
        s1.push(head);
        while (!s1.isEmpty()) {
            head = s1.pop();
            s2.push(head);
            if (head.left != null) {
                s1.push(head.left);
            }
            if (head.right != null) {
                s1.push(head.right);
            }
        }
        while (!s2.isEmpty()) {
            System.out.print(s2.pop().value + " ");
        }
    }
    System.out.println();
}

public static void posOrderUnRecur2(Node h) {
    System.out.print("pos-order: ");
    if (h != null) {
        Stack<Node> stack = new Stack<Node>();
        stack.push(h);
        Node c = null;
        while (!stack.isEmpty()) {
            c = stack.peek();
            if (c.left != null && h != c.left && h != c.right) {
                stack.push(c.left);
            } else if (c.right != null && h != c.right) {
                stack.push(c.right);
            } else {
                System.out.print(stack.pop().value + " ");
                h = c;
            }
        }
    }
    System.out.println();
}

public static void main(String[] args) {
    Node head = new Node(5);
    head.left = new Node(3);
    head.right = new Node(8);
    head.left.left = new Node(2);
    head.left.right = new Node(4);
    head.left.left.left = new Node(1);
    head.right.left = new Node(7);
    head.right.left.left = new Node(6);
    head.right.right = new Node(10);
    head.right.right.left = new Node(9);
    head.right.right.right = new Node(11);

    // recursive
    System.out.println("==============recursive==============");
    System.out.print("pre-order: ");
    preOrderRecur(head);
    System.out.println();
    System.out.print("in-order: ");
    inOrderRecur(head);
    System.out.println();
    System.out.print("pos-order: ");
    posOrderRecur(head);
    System.out.println();

    // unrecursive
    System.out.println("============unrecursive=============");
    preOrderUnRecur(head);
    inOrderUnRecur(head);
    posOrderUnRecur1(head);
    posOrderUnRecur2(head);

}

}