剑指offer:面试题21包含min函数的栈

Posted 2020-12-11 itxiaolei

题目描述

定义栈的数据结构，请在该类型中实现一个能够得到栈中所含最小元素的min函数（时间复杂度应为O（1））。
注意：保证测试中不会当栈为空的时候，对栈调用pop()或者min()或者top()方法。

代码示例

import java.util.Stack;

public class Offer21 {
    public static void main(String[] args) {
        Offer21 stack = new Offer21();
        stack.push(1);
        stack.push(2);
        stack.push(0);
        System.out.println(stack.min());
        stack.pop();
        System.out.println(stack.min());
        stack.pop();
        System.out.println(stack.min());
    }

    private Stack<Integer> dataStack = new Stack<>();
    private Stack<Integer> minStack = new Stack();

    public void push(int val) {
        dataStack.push(val);
        if (minStack.isEmpty()) {
            minStack.push(val);
        } else {
            minStack.push(Math.min(minStack.peek(), val));
        }
    }

    public void pop() {
        dataStack.pop();
        minStack.pop();
    }

    public int top() {
        return dataStack.peek();
    }

    public int min() {
        return minStack.peek();
    }
}