Stack_MiniStack.java

import java.util.Stack;

public class Stack_MiniStack {

    //声明一个data栈
    private static Stack<Integer> dataStack = new Stack<>();
    //声明一个min栈
    private static Stack<Integer> minStack = new Stack<>();

    //入栈
    public static void push(int num) {
        //1.入栈有两种情况
        //1.1 栈为空，那么第一个数直接进data栈和min栈
        //1.2 栈不为空，data栈正常入，入min栈的时候，先与min栈的栈顶数据进行比较，小的数入min栈
        if (dataStack.isEmpty()) {//栈为空
            dataStack.push(num);
            minStack.push(num);
        } else {//栈不为空
            dataStack.push(num);
            if (num < minStack.peek()) {
                minStack.push(num);
            } else {
                minStack.push(minStack.peek());
            }
        }
    }

    //弹栈
    public static Integer pop() {
        //弹栈的时候，data栈和min栈一起弹出，如果栈为空，则先提醒用户
        if (dataStack.isEmpty()) {
            throw new IllegalArgumentException("栈已空");
        }
        minStack.pop();
        return dataStack.pop();
    }

    //取最小值
    public static Integer getMin() {
        //直接获取最小栈的数据即可，如果栈为空，则先提醒用户
        if (dataStack.isEmpty()) {
            throw new IllegalArgumentException("栈已空");
        }
        return minStack.peek();
    }

    public static void main(String[] args) {
        int[] a = {1, 2, 3};
        for (int i = 0; i < a.length; i++) {
            push(a[i]);
            System.out.println(a[i] + " ");
        }
        System.out.println("pop:" + pop());
        System.out.println("getMini:" + getMin());
    }
}