package com.coding.week9;
/**
* 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];
private int pos1 = 0;
private int pos2 = data.length - 1;
/**
* 向第一个栈中压入元素
* @param o
*/
public void push1(Object o){
if (o == null) {
throw new RuntimeException("data can not be null");
}
data[pos1++] = o;
if (pos1 == pos2) {
doubleCapacity();
}
}
private void doubleCapacity(){
int oldCapacity = data.length;
int newCapacity = oldCapacity << 1;
if (newCapacity < 0) {
throw new RuntimeException("capacity is too large");
}
Object[] dataNew = new Object[newCapacity];
System.arraycopy(data, 0, dataNew, 0, pos1);
int moveNum = oldCapacity - pos2;
int newPos2 = newCapacity - moveNum;
System.arraycopy(data, pos2, dataNew, newPos2, moveNum);
pos2 = newPos2;
data = dataNew;
}
/**
* 从第一个栈中弹出元素
* @return
*/
public Object pop1(){
if (pos1 == 0) {
throw new RuntimeException("stack1 is empty");
}
Object e = data[--pos1];
data[pos1] = null;
return e;
}
/**
* 获取第一个栈的栈顶元素
* @return
*/
public Object peek1(){
if (pos1 == 0) {
return null;
}
return data[pos1 - 1];
}
/*
* 向第二个栈压入元素
*/
public void push2(Object o){
if (o == null) {
throw new RuntimeException("data can not be null");
}
data[pos2--] = o;
if (pos1 == pos2) {
doubleCapacity();
}
}
/**
* 从第二个栈弹出元素
* @return
*/
public Object pop2(){
if (pos2 == data.length - 1) {
throw new RuntimeException("stack2 is empty");
}
Object e = data[++pos2];
data[pos2] = null;
return e;
}
/**
* 获取第二个栈的栈顶元素
* @return
*/
public Object peek2(){
if (pos2 == data.length - 1) {
return null;
}
return data[pos2 + 1];
}
}