二叉树的遍历使用Java实现

import java.util.Stack;

/**
 * Created by ***** on 2017/8/21.
 */
public class BinaryTreeSeek {
    public static void main(String[] agrs){
        BinarySortTree b = new BinarySortTree();
        b.val = 5;
        b.left_child = new BinarySortTree();
        b.right_child = new BinarySortTree();
        b.left_child.val = 3;
        b.right_child.val = 7;
        b.left_child.left_child = new BinarySortTree();
        b.left_child.right_child = new BinarySortTree();
        b.left_child.left_child.val = 2;
        b.left_child.right_child.val = 4;
        b.right_child.left_child = new BinarySortTree();
        b.right_child.right_child = new BinarySortTree();
        b.right_child.left_child.val = 6;
        b.right_child.right_child.val = 8;

//        PreOrder(b);
//        System.out.println();
//        PreOrder2(b);
//        System.out.println();
//        InOrder(b);
//        System.out.println();
//        InOrder2(b);
//        System.out.println();
//        PostOrder(b);
//        System.out.println();
        PostOrder2(b);
    }

    /**
     * 二叉树递归前序遍历
     * @param tree
     */
    public static void PreOrder(BinarySortTree tree){
        if (tree != null){
            System.out.print(tree.val+" ");
            PreOrder(tree.left_child);
            PreOrder(tree.right_child);
        }else {
            return;
        }
    }

    /**
     * 二叉树前序遍历
     * @param tree
     */
    public static void PreOrder2(BinarySortTree tree){
        Stack<BinarySortTree> stack = new Stack<>();
        while(tree != null || !stack.empty()){
            if (tree != null){
                stack.push(tree);
                System.out.print(tree.val+" ");
                tree = tree.left_child;
            }else {
                tree = stack.pop();
                tree = tree.right_child;
            }

        }
    }


    /**
     * 二叉树递归中序遍历
     * @param tree
     */
    public static void InOrder(BinarySortTree tree){
        if (tree != null){
            InOrder(tree.left_child);
            System.out.print(tree.val+" ");
            InOrder(tree.right_child);
        }else {
            return;
        }
    }

    /**
     * 二叉树中序遍历
     * @param tree
     */
    public static void InOrder2(BinarySortTree tree){
        Stack<BinarySortTree> stack = new Stack<>();
        while(tree != null || !stack.empty()){
            if (tree != null){
                stack.push(tree);
                tree = tree.left_child;
            }else {
                tree = stack.pop();
                System.out.print(tree.val+" ");
                tree = tree.right_child;
            }

        }
    }

    /**
     * 二叉树递归后序遍历
     * @param tree
     */
    public static void PostOrder(BinarySortTree tree){
        if (tree != null){
            PostOrder(tree.left_child);
            PostOrder(tree.right_child);
            System.out.print(tree.val+" ");
        }else {
            return;
        }
    }

    /**
     * 二叉树后序遍历 需要记录上一次弹出的节点
     * @param tree
     */
    public static void PostOrder2(BinarySortTree tree){
        Stack<BinarySortTree> stack = new Stack<>();
        BinarySortTree lastview = null;
        while(tree != null || !stack.empty()){
            if (tree != null){
                stack.push(tree);
                tree = tree.left_child;
            }else {
                tree = stack.pop();
                if (tree.right_child == null || tree.right_child == lastview){
                    //如果无右节点或者该节点的右节点已经访问过
                    System.out.print(tree.val+" ");
                    lastview = tree;
                    tree = null;
                }else {
                    stack.push(tree);//重新入栈有右孩子的改节点
                    tree = tree.right_child;
                }

            }

        }
    }
}