package week09.basic;
import java.util.EmptyStackException;
import java.util.Stack;
/**
* 设计一个栈,支持栈的push和pop操作,以及第三种操作findMin, 它返回改数据结构中的最小元素
* finMin操作最坏的情形下时间复杂度应该是O(1) , 简单来讲,操作一次就可以得到最小值
* @author gallenzhang
*
*/
public class QuickMinStack {
Stack<Integer> stack = new Stack<>();
Stack<Integer> minStack = new Stack<>();
public void push(int data) {
stack.push(data);
if(minStack.isEmpty()){
minStack.push(data);
return ;
}
if(minStack.peek() > data){
minStack.push(data);
}
}
public int pop() {
if(stack.isEmpty()){
throw new EmptyStackException();
}
int item = stack.pop();
if(item == minStack.peek()){
minStack.pop();
}
return item;
}
public int findMin() {
if(minStack.isEmpty()){
throw new EmptyStackException();
}
return minStack.peek();
}
}