首先：二叉树的建立
首先，我们采用广义表建立二叉树（关于广义表的概念，请查看百科的介绍：http://baike.baidu.com/view/203611.htm）
我们建立一个字符串类型的广义表作为输入：
String expression = "A(B(D(,G)),C(E,F))";与该广义表对应的二叉树为
1366533767_1515.jpg
写代码前，我们通过观察二叉树和广义表，先得出一些结论：
每当遇到字母，将要创建节点
每当遇到“（”，表面要创建左孩子节点
每当遇到“，”，表明要创建又孩子节点
每当遇到“）”，表明要返回上一层节点
广义表中“（”的数量正好是二叉树的层数
节点类的构建###
public class Node {
private char data;
private Node lchild;
private Node rchild;
public Node(){
}
public char getData() {
return data;
}
public void setData(char data) {
this.data = data;
}
public Node getRchild() {
return rchild;
}
public void setRchild(Node rchild) {
this.rchild = rchild;
}
public Node getLchild() {
return lchild;
}
public void setLchild(Node lchild) {
this.lchild = lchild;
}
public Node(char ch, Node rchild, Node lchild) {
this.data = ch;
this.rchild = rchild;
this.lchild = lchild;
}
public String toString() {
return "" + getData();
}
}
创建二叉树###
public Node createTree(String exp) {
Node[] nodes = new Node[3];
Node b, p = null;
int top = -1, k = 0, j = 0;
char[] exps = exp.toCharArray();
char data = exps[j];
b = null;
while (j < exps.length - 1) {
switch (data) {
case '(':
top++;
nodes[top] = p;
k = 1;
break;
case ')':
top--;
break;
case ',':
k = 2;
break;
default:
p = new Node(data, null, null);
if (b == null) {
b = p;
} else {
switch (k) {
case 1:
nodes[top].setLchild(p);
break;
case 2:
nodes[top].setRchild(p);
break;
}
}
}
j++;
data = exps[j];
}
return b;
}
递归执行三种遍历###
/**
* pre order recursive
*
* @param node
*/
public void PreOrder(Node node) {
if (node == null) {
return;
} else {
System.out.print(node.getData() + " ");
PreOrder(node.getLchild());
PreOrder(node.getRchild());
}
}
/**
* in order recursive
*
* @param node
*/
public void InOrder(Node node) {
if (node == null) {
return;
} else {
InOrder(node.getLchild());
System.out.print(node.getData() + " ");
InOrder(node.getRchild());
}
}
/**
* post order recursive
*
* @param node
*/
public void PostOrder(Node node) {
if (node == null) {
return;
} else {
PostOrder(node.getLchild());
PostOrder(node.getRchild());
System.out.print(node.getData() + " ");
}
}
非递归遍历###
前序遍历
public void PreOrderNoRecursive(Node node) {
Node nodes[] = new Node[CAPACITY];
Node p = null;
int top = -1;
if (node != null) {
top++;
nodes[top] = node;
while (top > -1) {
p = nodes[top];
top--;
System.out.print(p.getData() + " ");
if (p.getRchild() != null) {
top++;
nodes[top] = p.getRchild();
}
if (p.getLchild() != null) {
top++;
nodes[top] = p.getLchild();
}
}
}
}
中序遍历
public void InOrderNoRecursive(Node node) {
Node nodes[] = new Node[CAPACITY];
Node p = null;
int top = -1;
if (node != null)
p = node;
while (p != null || top > -1) {
while (p != null) {
top++;
nodes[top] = p;
p = p.getLchild();
}
if (top > -1) {
p = nodes[top];
top--;
System.out.print(p.getData() + " ");
p = p.getRchild();
}
}
}
后序遍历
public void PostOrderNoRecursive(Node node) {
Node[] nodes = new Node[CAPACITY];
Node p = null;
int flag = 0, top = -1;
if (node != null) {
do {
while (node != null) {
top++;
nodes[top] = node;
node = node.getLchild();
}
p = null;
flag = 1;
while (top != -1 && flag != 0) {
node = nodes[top];
if (node.getRchild() == p) {
System.out.print(node.getData() + " ");
top--;
p = node;
} else {
node = node.getRchild();
flag = 0;
}
}
} while (top != -1);
}
}