返回栈中最小元素的两种实现O(1)

package arithmetic;

import java.util.Stack;

public class GetMinStack {

    //省空间，费时间
    public static class MyStack1 {
        private Stack<Integer> stackData;
        private Stack<Integer> stackMin;

        public MyStack1() {
            stackData = new Stack<>();
            stackMin = new Stack<>();
        }

        public void push(int value) {
            if (this.stackMin.isEmpty()) {
                stackMin.push(value);
            } else if (value <= getmin()) {
                stackMin.push(value);
            }
            this.stackData.push(value);
        }

        public int pop() {
            if (this.stackData.isEmpty()) {
                throw new RuntimeException("Your stack is empty.");
            }
            int res = this.stackData.pop();
            if (res == getmin()) {
                this.stackMin.pop();
            }
            return res;
        }

        public int getmin() {
            if (this.stackMin.isEmpty()) {
                throw new RuntimeException("Your stack is empty.");
            }
            return this.stackMin.peek();
        }
    }

    //省时间，费空间
    public static class MyStack2 {
        private Stack<Integer> stackData;
        private Stack<Integer> stackMin;

        public MyStack2() {
            this.stackData = new Stack<Integer>();
            this.stackMin = new Stack<Integer>();
        }

        public void push(int value) {
            if (stackMin.isEmpty()) {
                stackMin.push(value);
            }
            if (value <= getmin()) {
                stackMin.push(value);
            } else {
                stackMin.push(getmin());
            }
            stackData.push(value);
        }

        public int pop() {
            if (this.stackData.isEmpty()) {
                throw new RuntimeException("Your stack is empty.");
            }
            stackMin.pop();
            return stackData.pop();
        }

        public int getmin() {
            if (this.stackMin.isEmpty()) {
                throw new RuntimeException("Your stack is empty.");
            }
            return this.stackMin.peek();
        }
    }

    public static void main(String[] args) {
        MyStack1 stack1 = new MyStack1();
        stack1.push(3);
        System.out.println(stack1.getmin());
        stack1.push(4);
        System.out.println(stack1.getmin());
        stack1.push(1);
        System.out.println(stack1.getmin());
        System.out.println(stack1.pop());
        System.out.println(stack1.getmin());

        System.out.println("=============");

        MyStack1 stack2 = new MyStack1();
        stack2.push(3);
        System.out.println(stack2.getmin());
        stack2.push(4);
        System.out.println(stack2.getmin());
        stack2.push(1);
        System.out.println(stack2.getmin());
        System.out.println(stack2.pop());
        System.out.println(stack2.getmin());
    }
}