【二叉树】二叉树遍历

import lombok.Data;
import lombok.NoArgsConstructor;

import java.util.LinkedList;

/**
 * @author Joeson Chan
 */
public class Traverse {

    @Data
    @NoArgsConstructor
    public static class Node {

        public Node(String data, Node lc, Node rc) {
            this.data = data;
            this.lc = lc;
            this.rc = rc;
        }

        private String data;
        private Node lc;
        private Node rc;
    }

    /**
     * 前序遍历递归
     */
    public static void preDiv(Node node){
        if(null == node){
            return;
        }

        System.out.print(node.data + " ");
        preDiv(node.lc);
        preDiv(node.rc);
    }

    /**
     * 中序遍历递归
     * @param node
     */
    public static void midDiv(Node node){
        if(null == node){
            return;
        }

        midDiv(node.lc);
        System.out.print(node.data + " ");
        midDiv(node.rc);
    }

    /**
     * 后序遍历递归
     */
    public static void postDiv(Node node){
        if(null == node){
            return;
        }

        midDiv(node.lc);
        midDiv(node.rc);
        System.out.print(node.data + " ");
    }

    /**
     * 先序遍历
     */
    public static void pre(Node root) {
        if (null == root) {
            return;
        }

        LinkedList<Node> stack = new LinkedList<>();
        Node node = root;
        while (node != null || !stack.isEmpty()) {
            if (node != null) {
                System.out.print(node.data + "  ");
                stack.push(node);
                node = node.lc;
            } else { //pNode == null && !stack.isEmpty()
                node = stack.pop();
                node = node.rc;
            }
        }
    }

    /**
     * 中序遍历
     */
    public static void mid(Node root) {
        if (null == root) {
            return;
        }

        LinkedList<Node> stack = new LinkedList<>();
        Node node = root;
        while (null != node || !stack.isEmpty()) {
            if (node != null) {
                stack.push(node);
                node = node.lc;
            } else { //pNode == null && !stack.isEmpty()
                node = stack.pop();
                System.out.print(node.data + "  ");
                node = node.rc;
            }
        }
    }


    /**
     * 后续遍历
     */
    public static void post(Node root) {
        if (null == root) {
            return;
        }

        LinkedList<Node> stack = new LinkedList<>();
        LinkedList<Node> output = new LinkedList<>();
        Node node = root;
        while (node != null || stack.size() > 0) {
            if (node != null) {
                output.push(node);
                stack.push(node);
                node = node.rc;
            } else {
                node = stack.pop();
                node = node.lc;
            }
        }

        while (output.size() > 0) {
            System.out.print(output.pop().data + "  ");
        }
    }

    private static Node mock() {
        Node F = new Node("F", null, null);
        Node E = new Node("E", null, null);
        Node B = new Node("B", F, E);
        Node G = new Node("G", null, null);
        Node H = new Node("H", null, null);
        Node C = new Node("C", G, H);
        Node A = new Node("A", B, C);
        return A;
    }

    private static void testPre() {
        preDiv(mock());
        System.out.println();
    }

    private static void testMid() {
        midDiv(mock());
        System.out.println();
    }

    private static void testPost() {
        post(mock());
        System.out.println();
    }

    public static void main(String[] args) {
        testPre();
        testMid();
        testPost();
    }
}