栈的定义
栈（stack）又名堆栈，它是一种运算受限的线性表。限定仅在表尾进行插入和删除操作的线性表。这一端被称为栈顶，相对地，把另一端称为栈底。向一个栈插入新元素又称作进栈、入栈或压栈，它是把新元素放到栈顶元素的上面，使之成为新的栈顶元素；从一个栈删除元素又称作出栈或退栈，它是把栈顶元素删除掉，使其相邻的元素成为新的栈顶元素。
栈的顺序存储实现
package algorithm.datastructure.stack;
/*
* 栈
* 一种特殊的线性表—-操作受限的线性表，限于在表尾插入或删除元素的线性表
* 顺序栈
* 采用一段连续的空间存储(数组)
*
* */
public class SeqStack {
private int []table;//数组
private int top;//栈顶元素
private int maxSize;//栈的容量
private int size;//当前栈的元素个数
private int incrementCapacity;//扩容时增长容量
private static final int STACK_DEFAULT_INIT_SIZE=10;//初始容量
private static final int STACK_DEFAULT_INCREMENT_SIZE=5;//扩容时默认增长容量
//栈的初始化
public SeqStack(){
this.maxSize=STACK_DEFAULT_INIT_SIZE;
this.table=new int[maxSize];
this.top=-1;
this.incrementCapacity=STACK_DEFAULT_INCREMENT_SIZE;
}
public SeqStack(int initialCapacity){
this.maxSize=initialCapacity;
this.table=new int[maxSize];
this.incrementCapacity=STACK_DEFAULT_INCREMENT_SIZE;
this.top=-1;
}
public SeqStack(int initialCapacity,int incrementCapacity){
this.maxSize=initialCapacity;
this.table=new int[maxSize];
this.incrementCapacity=incrementCapacity;
this.top=-1;
}
//判断栈是否为空
public Boolean isEmpty(){
return top==-1;
}
//判断栈是否满
public Boolean isFull(){
return (maxSize-1)==top;
}
//插入一个元素
public void push(int x){
if (isFull()){
ensureCapacity();
table[++top]=x;
size++;
} else {
table[++top]=x;
size++;
}
}
//删除一个元素
public Integer pop(){
if (isEmpty()){
try {
throw new Exception("栈空");
} catch (Exception e) {
e.printStackTrace();
}
} else {
size--;
return table[top--];
}
return null;
}
//得到栈顶元素
public Integer getTop(){
if (isEmpty()){
try {
throw new Exception("栈空");
} catch (Exception e) {
e.printStackTrace();
}
} else {
return table[top];
}
return null;
}
//获取当前栈中元素个数
public int size(){
return size;
}
//扩容
private void ensureCapacity() {
System.out.println("当前栈的容量为:"+maxSize+"，容量不足，扩容");
maxSize=maxSize+incrementCapacity;
int []newTable=new int[maxSize];
for (int i=0;i<table.length;i++){
//将旧数组的元素移到新数组
newTable[i]=table[i];
}
table=newTable;
System.out.println("扩容成功，扩容后栈的新容量为:"+maxSize);
}
public static void main(String[] args) {
//SeqStack seqStack=new SeqStack(10,2);
// SeqStack seqStack=new SeqStack();
SeqStack seqStack=new SeqStack(15);
seqStack.push(1);
seqStack.push(2);
seqStack.push(4);
seqStack.push(4);
seqStack.push(5);
seqStack.push(1);
seqStack.push(2);
seqStack.push(4);
seqStack.push(4);
seqStack.push(5);
seqStack.push(1);
seqStack.push(2);
seqStack.push(4);
seqStack.push(4);
seqStack.push(5);
System.out.println(seqStack.pop());
System.out.println(seqStack.pop());
System.out.println(seqStack.pop());
System.out.println(seqStack.pop());
System.out.println(seqStack.pop());
System.out.println(seqStack.pop());
System.out.println(seqStack.getTop());
System.out.println(seqStack.getTop());
System.out.println(seqStack.getTop());
System.out.println(seqStack.size());
}
}
栈的链式存储实现
package algorithm.datastructure.stack;
/*
* 栈
* 一种特殊的线性表—-操作受限的线性表，限于在表尾插入或删除元素的线性表
* 链栈
* 采用非连续的空间存储
* */
public class LinkedStack {
private Node top;//栈顶指针
private Node bottom;//栈底指针
private Integer size;//栈的当前大小
private static class Node{
int data;
Node next;
public Node(){
}
public Node(int data){
this.data=data;
this.next=null;
}
public Node(int data,Node next){
this.data=data;
this.next=next;
}
}
public LinkedStack(){
top=new Node();
bottom=new Node();
top.next=bottom;
size=0;
}
public Boolean isEmpty(){
return top.next==bottom;
}
//插入元素
public void push(int x){
top= new Node(x,top);
size++;
}
//删除元素
public Integer pop(){
if (isEmpty()){
try {
throw new Exception("栈空");
}catch (Exception e){
e.printStackTrace();
}
} else {
Node x=top;
top=x.next;
size--;
return x.data;
}
return null;
}
public Integer getTop(){
if (isEmpty()){
try {
throw new Exception("栈空");
}catch (Exception e){
e.printStackTrace();
}
} else {
return top.data;
}
return null;
}
//获取当前栈中元素个数
public int size(){
return size;
}
public static void main(String[] args) {
//测试
LinkedStack linkedStack=new LinkedStack();
linkedStack.push(1);
linkedStack.push(2);
linkedStack.push(4);
linkedStack.push(5);
linkedStack.push(7);
linkedStack.push(9);
System.out.println(linkedStack.size());
System.out.println(linkedStack.pop());
System.out.println(linkedStack.pop());
System.out.println(linkedStack.getTop());
System.out.println(linkedStack.getTop());
// System.out.println(linkedStack.pop());
}
}