剑指offer 20. 举例让抽象具体化 包含min函数的栈

import java.util.Stack;
import java.util.Arrays;
public class Solution {

private int size;
private Stack<Integer> minStack=new Stack<Integer>();
private int min=Integer.MAX_VALUE;
private Integer[] elements = new Integer[10];

private void ensureCapacity(int size) {
// TODO Auto-generated method stub
int len = elements.length;
if(size > len){
int newLen = (len*3)/2+1; //每次扩容方式
elements = Arrays.copyOf(elements, newLen);
}
}

public void push(int node) {
ensureCapacity(size+1);
elements[size++]=node;
if (node<=min) {
minStack.push(node);
min=minStack.peek();
}else {
minStack.push(min);
}

}

public void pop() {
Integer top=top();
if (top!=null) {
elements[size-1]=(Integer)null;
}
size--;
minStack.pop();
min=minStack.peek();

}

public int top() {

if(!empty()){
if(size-1>=0)
return elements[size-1];
}
return (Integer) null;

}
public boolean empty(){
return size == 0;
}
public int min() {

return min;

}
}