package com.github.HarryHook.coding2017.stack;
import java.util.Arrays;
/**
* 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 HarryHook
*
*/
public class TwoStackInOneArray {
Object[] data = new Object[6];
int i = 0;
int j = data.length - 1;
/**
* 向第一个栈中压入元素
*
* @param o
*/
public void push1(Object o) {
if (i > j) {
expansion();
}
data[i++] = o;
}
/**
* 从第一个栈中弹出元素
*
* @return
*/
public Object pop1() {
if (data[0] == null) {
throw new RuntimeException("stack1 is empty");
}
Object tmp = data[i - 1];
data[--i] = null;
return tmp;
}
/**
* 获取第一个栈的栈顶元素
*
* @return
*/
public Object peek1() {
return data[i - 1];
}
/*
* 向第二个栈压入元素
*/
public void push2(Object o) {
if (i > j) {
expansion();
}
data[j--] = o;
}
/**
* 从第二个栈弹出元素
*
* @return
*/
public Object pop2() {
if (data[data.length - 1] == null) {
throw new RuntimeException("stack2 is empty");
}
Object tmp = data[j + 1];
data[++j] = null;
return tmp;
}
/**
* 获取第二个栈的栈顶元素
*
* @return
*/
public Object peek2() {
return data[j + 1];
}
// 给数组扩容
public void expansion() {
int oldCapacity = data.length;
int newCapacity = oldCapacity * 2; // 此时扩容是因为数组有可能全是stack2的元素
data = Arrays.copyOf(data, newCapacity);
int newIndex = newCapacity - 1;
for (int k = oldCapacity - 1; k > j; k--) {
data[newIndex--] = data[k];
data[k] = null;
}
j += newCapacity - oldCapacity;
}
public static void main(String[] args) {
TwoStackInOneArray stack = new TwoStackInOneArray();
stack.push1(3);
stack.push1(5);
stack.push1(6);
stack.push1(11);
System.out.println("peek1: " + stack.peek1());
System.out.println("pop1: " + stack.pop1());
System.out.println("pop1: " + stack.pop1());
stack.push1(61);
System.out.println("pop1: " + stack.pop1());
System.out.println("pop1: " + stack.pop1());
System.out.println("peek1: " + stack.peek1());
System.out.println("pop1: " + stack.pop1());
stack.push2(123);
stack.push2(1);
stack.push2(4);
stack.push1(3);
stack.push1(5);
stack.push1(6);
stack.push2(123);
stack.push2(1);
stack.push2(4);
stack.push2(12);
stack.push2(2);
stack.push2(8);
System.out.println("pop1: " + stack.pop1());
System.out.println("peek1: " + stack.peek1());
System.out.println("pop1: " + stack.pop1());
System.out.println("pop1: " + stack.pop1());
System.out.println("pop2: " + stack.pop2());
System.out.println("pop2: " + stack.pop2());
System.out.println("pop2: " + stack.pop2());
System.out.println("pop2: " + stack.pop2());
System.out.println("pop2: " + stack.pop2());
System.out.println("pop2: " + stack.pop2());
System.out.println("pop2: " + stack.pop2());
System.out.println("pop2: " + stack.pop2());
System.out.println("pop2: " + stack.pop2());
}
}