package com.donaldy.basic.stack;
/**
* 用一个数组实现两个栈
* 将数组的起始位置看作是第一个栈的栈底，将数组的尾部看作第二个栈的栈底，
* 压栈时，栈顶指针分别向中间移动，直到两栈顶指针相遇，则扩容。
* @author liuxin
*
*/
public class TwoStackInOneArray {
Object[] data = new Object[10];
/**
* 0, 10用来存储指针，
* 用于判断 栈是否为空
*/
int pointer1 = 0;
int pointer2= 9;
/**
* 向第一个栈中压入元素
* @param o
*/
public void push1(Object o){
ensureCapacity();
this.data[++ this.pointer1] = o;
}
/**
* 扩容后，pointer1指针不变，pointer2指针要改变
* 注意复制
*/
private void ensureCapacity() {
if (this.pointer1 + 1 == this.pointer2 || this.pointer1 == this.pointer2 + 1) {
int newCapacity = this.data.length * 2 + 1;
Object[] newDataArray = new Object[newCapacity];
System.arraycopy(this.data, 1, newDataArray, 1, this.pointer1);
int pointer2Len = this.data.length - 1 - this.pointer2;
System.arraycopy(this.data, this.pointer2, newDataArray,
newCapacity - pointer2Len - 1, pointer2Len);
this.pointer2 = newCapacity - pointer2Len - 1;
this.data = newDataArray;
}
}
/**
* 从第一个栈中弹出元素
* @return
*/
public Object pop1() {
if (this.pointer1 <= 0 || this.pointer1 >= this.data.length) {
throw new IndexOutOfBoundsException("size : " + this.pointer1);
}
return this.data[this.pointer1 --];
}
/**
* 获取第一个栈的栈顶元素
* @return
*/
public Object peek1(){
if (this.pointer1 <= 0 || this.pointer1 >= this.data.length) {
throw new IndexOutOfBoundsException("size : " + this.pointer1);
}
return this.data[this.pointer1];
}
/**
* 向第二个栈压入元素
*/
public void push2(Object o){
ensureCapacity();
System.out.println("push : " + o);
this.data[-- this.pointer2] = o;
}
/**
* 从第二个栈弹出元素
* @return
*/
public Object pop2(){
if (this.pointer2 >= this.data.length || this.pointer2 <= 0) {
throw new IndexOutOfBoundsException("size : " + this.pointer2);
}
return this.data[this.pointer2 ++];
}
/**
* 获取第二个栈的栈顶元素
* @return
*/
public Object peek2(){
if (this.pointer2 >= this.data.length || this.pointer2 <= 0) {
throw new IndexOutOfBoundsException("size : " + this.pointer2);
}
return this.data[this.pointer2];
}
}