用Java实现二叉树的三种遍历方式

二叉树如下：

遍历结果如下：

以下是实现代码：

package binTree;

import java.util.Stack;

/**
 * @author bin.zhang
 * @version 2017年8月29日 上午10:22:01
 */
public class BinTreeTraversal {
    public static void main(String[] args) {
        System.out.print("前序：");
        Traversal.preOrder();
        Traversal.preOrderRecursion(Traversal.createBinTree());
        System.out.print("中序：");
        Traversal.inOrder();
        Traversal.inOrderRecursion(Traversal.createBinTree());
        System.out.print("后序：");
        Traversal.postOrder();
        Traversal.postOrderRecursion(Traversal.createBinTree());
    }
}

/**
 * 节点数据结构
 * 
 * @author bin.zhang
 * @version 2017年8月30日 上午11:49:38
 */
class BinTreeNode {

    BinTreeNode() {
    }

    BinTreeNode(char data, int flag, BinTreeNode lchild, BinTreeNode rchild) {
        this.data = data;
        this.flag = flag;
        this.lchild = lchild;
        this.rchild = rchild;
    }

    char data;
    int flag;
    BinTreeNode lchild, rchild;

}

class Traversal {

    /**
     * 创建一棵二叉树
     * 
     * @author bin.zhang
     * @return 根节点
     */
    public static BinTreeNode createBinTree() {
        BinTreeNode R3 = new BinTreeNode('F', 0, null, null);
        BinTreeNode L2 = new BinTreeNode('D', 0, null, null);
        BinTreeNode R2 = new BinTreeNode('E', 0, null, R3);
        BinTreeNode L1 = new BinTreeNode('B', 0, L2, R2);
        BinTreeNode R1 = new BinTreeNode('C', 0, null, null);
        BinTreeNode T = new BinTreeNode('A', 0, L1, R1);
        return T;
    }

    // 前序
    public static void preOrder() {

        BinTreeNode p = createBinTree();

        Stack stack = new Stack();

        while (p != null || !stack.empty()) {
            if (p != null) {
                System.out.print(p.data);
                stack.push(p);
                p = p.lchild;
            }
            else {
                p = stack.pop();
                p = p.rchild;
            }
        }
        System.out.println();

    }

    // 前序递归
    public static void preOrderRecursion(BinTreeNode top) {
        if (top != null) {
            System.out.println(top.data);
            preOrderRecursion(top.lchild);
            preOrderRecursion(top.rchild);
        }
    }

    // 中序
    public static void inOrder() {

        BinTreeNode p = createBinTree();

        Stack stack = new Stack();

        while (p != null || !stack.empty()) {
            if (p != null) {
                stack.push(p);
                p = p.lchild;
            }
            else {
                p = stack.pop();
                System.out.print(p.data);
                p = p.rchild;
            }
        }
        System.out.println();
    }

    // 中序递归
    public static void inOrderRecursion(BinTreeNode top) {
        if (top != null) {
            inOrderRecursion(top.lchild);
            System.out.println(top.data);
            inOrderRecursion(top.rchild);
        }
    }

    // 后序
    public static void postOrder() {

        BinTreeNode p = createBinTree();

        Stack stack = new Stack(); // 初始化栈

        int mark = 1; // 转向标志
        while (p != null || !stack.empty()) { // 遍历
            if (p != null && mark != 0) {
                stack.push(p);
                p = p.lchild;
            }// 转向左子树
            else {
                p = stack.pop();
                p.flag++; // 退栈
                if (p.flag == 1) {
                    stack.push(p);
                    p = p.rchild;
                    mark = 1;
                } // 转向右子树
                else if (p.flag == 2 && !stack.empty()) { // 输出结点
                    System.out.print(p.data);
                    mark = 0;
                }
                else if (p.flag == 2 && stack.empty()) { // 输出根结点并退出
                    System.out.print(p.data);
                    break;
                }
            } // if-else
        } // while
        System.out.println();
    }

    // 后序递归
    public static void postOrderRecursion(BinTreeNode top) {
        if (top != null) {
            postOrderRecursion(top.lchild);
            postOrderRecursion(top.rchild);
            System.out.println(top.data);
        }
    }
}