算法 - 遍历二叉树- 递归和非递归

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.data);
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.data);
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.data);
}

// 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);
}
}