栈，队列和二叉树的实现

1.栈

public class Stack {

private T[] arr = (T[]) new Object[1];

private int n = 0;

public boolean isEmpty(){

return n == 0;

}

public int size(){

return n;

}

public void resize(int max){

T[] temp = (T[]) new Object[max];

for(int i = 0; i < n; i++){

temp[i] = arr[i];

}

arr = temp;

}

public boolean push(T t){

if(n == arr.length){

resize(n*2);

}

arr[n++] = t;

return true;

}

public T pop(){

if(isEmpty()){

//空栈

return null;

}

if(n <= arr.length/4){

//调整栈的大小

resize(arr.length/2);

}

return arr[--n];

}

}

2.队列

public class Queue {

private Node head;

private Node tail;

private int n = 0;

private class Node{

T value;

Node nextNode;

}

public boolean isEmpty(){

return n == 0;

}

public int size(){

return n;

}

public boolean enQueue(T t){

Node oldLast = tail;

tail = new Node();

tail.value = t;

tail.nextNode = null;

if(isEmpty()){

head =tail;

}else{

oldLast.nextNode = tail;

}

n++;

return true;

}

public T deQueue(){

if(isEmpty()){

//队列为空

return null;

}

Node lastHead = head;

head = head.nextNode;

n--;

return lastHead.value;

}

}

3 二叉树

public class TreeNode {

private T value;

private TreeNode leftNode;

private TreeNode rightNode;

public void init(T t){

value = t;

}

public TreeNode findNode(T t){

if(t.equals(value)){

return this;

}

TreeNode ptr = null;

if(leftNode != null){

if((ptr=leftNode.findNode( t)) != null){

return ptr;

}

}

if(rightNode != null){

if((ptr = rightNode.findNode( t)) != null){

return ptr;

}

}

return null;

}

public boolean insert( T t){

TreeNode node = new TreeNode<>();

node.value = t;

if(leftNode == null){

leftNode = node;

return true;

}

if(rightNode == null){

rightNode = node;

return true;

}

return false;

}

public int depth(){

if(leftNode == null && rightNode == null){

return 1;

}

int leftDepth = leftNode.depth();

int rightDepth = rightNode.depth();

return leftDepth > rightDepth ? leftDepth+1 :rightDepth+1;

}

public void levelTree(){

//节点队列

Queue> queue = new Queue<>();

//值队列

Queue valueQueue = new Queue<>();

//根节点的值加入值队列

valueQueue.enQueue(this.value);

//左子节点加入队列

if(leftNode != null){

queue.enQueue(leftNode);

}

//右子节点加入队列

if(rightNode != null){

queue.enQueue(rightNode);

}

while(!queue.isEmpty()){

TreeNode node = queue.deQueue();

if(node.leftNode != null){

queue.enQueue(node.leftNode);

}

if(node.rightNode != null){

queue.enQueue(node.rightNode);

}

valueQueue.enQueue(node.value);

}

while(!valueQueue.isEmpty()){

System.out.println(valueQueue.deQueue());

}

}

public void leftTree(){

if(leftNode != null){

leftNode.leftTree();

}

System.out.println(this.value);

if(rightNode != null){

rightNode.leftTree();

}

}

public void midTree(){

System.out.println(this.value);

if(leftNode != null){

leftNode.midTree();

}

if(rightNode != null){

rightNode.midTree();

}

}

}