JAVA递归、非递归遍历二叉树（转）

原文链接： JAVA递归、非递归遍历二叉树

import java.util.Stack;
import java.util.HashMap;  

public class BinTree {
    private char date;
    private BinTree lchild;
    private BinTree rchild;  

    public BinTree(char c) {
        date = c;
    }  

    // 先序遍历递归
    public static void preOrder(BinTree t) {
        if (t == null) {
            return;
        }
        System.out.print(t.date);
        preOrder(t.lchild);
        preOrder(t.rchild);
    }  

    // 中序遍历递归
    public static void InOrder(BinTree t) {
        if (t == null) {
            return;
        }
        InOrder(t.lchild);
        System.out.print(t.date);
        InOrder(t.rchild);
    }  

    // 后序遍历递归
    public static void PostOrder(BinTree t) {
        if (t == null) {
            return;
        }
        PostOrder(t.lchild);
        PostOrder(t.rchild);
        System.out.print(t.date);
    }  

    // 先序遍历非递归
    public static void preOrder2(BinTree t) {
        Stack<BinTree> s = new Stack<BinTree>();
        while (t != null || !s.empty()) {
            while (t != null) {
                System.out.print(t.date);
                s.push(t);
                t = t.lchild;
            }
            if (!s.empty()) {
                t = s.pop();
                t = t.rchild;
            }
        }
    }  

    // 中序遍历非递归
    public static void InOrder2(BinTree t) {
        Stack<BinTree> s = new Stack<BinTree>();
        while (t != null || !s.empty()) {
            while (t != null) {
                s.push(t);
                t = t.lchild;
            }
            if (!s.empty()) {
                t = s.pop();
                System.out.print(t.date);
                t = t.rchild;
            }
        }
    }  

    // 后序遍历非递归
    public static void PostOrder2(BinTree t) {
        Stack<BinTree> s = new Stack<BinTree>();
        Stack<Integer> s2 = new Stack<Integer>();
        Integer i = new Integer(1);
        while (t != null || !s.empty()) {
            while (t != null) {
                s.push(t);
                s2.push(new Integer(0));
                t = t.lchild;
            }
            while (!s.empty() && s2.peek().equals(i)) {
                s2.pop();
                System.out.print(s.pop().date);
            }  

            if (!s.empty()) {
                s2.pop();
                s2.push(new Integer(1));
                t = s.peek();
                t = t.rchild;
            }
        }
    }  

    public static void main(String[] args) {
        BinTree b1 = new BinTree('a');
        BinTree b2 = new BinTree('b');
        BinTree b3 = new BinTree('c');
        BinTree b4 = new BinTree('d');
        BinTree b5 = new BinTree('e');  

        /**
         *      a
         *     / /
         *    b   c
         *   / /
         *  d   e
         */
        b1.lchild = b2;
        b1.rchild = b3;
        b2.lchild = b4;
        b2.rchild = b5;  

        BinTree.preOrder(b1);
        System.out.println();
        BinTree.preOrder2(b1);
        System.out.println();
        BinTree.InOrder(b1);
        System.out.println();
        BinTree.InOrder2(b1);
        System.out.println();
        BinTree.PostOrder(b1);
        System.out.println();
        BinTree.PostOrder2(b1);
    }
}