You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation. Evaluate the expression. Return an integer that represents the value of the expression. Note that:

Given an array of integers temperatures represents the daily temperatures, return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible…

你有一个只支持单个标签页的 浏览器 ，最开始你浏览的网页是 homepage ，你可以访问其他的网站 url ，也可以在浏览历史中后退 steps 步或前进 steps 步。 请你实现 BrowserHistory 类：

请你设计一个带光标的文本编辑器，它可以实现以下功能：

给你一个字符串 s ，下标从 0 开始 ，且长度为偶数 n 。字符串 恰好 由 n / 2 个开括号 '[' 和 n / 2 个闭括号 ']' 组成。 只有能满足下述所有条件的字符串才能称为 平衡字符串 ：

一个括号字符串是只由 '(' 和 ')' 组成的 非空 字符串。如果一个字符串满足下面 任意 一个条件，那么它就是有效的：

You are given an array nums of n positive integers and an integer k. Initially, you start with a score of 1. You have to maximize your score by applying the following operation at most k times:

给你一个字符串 s 和一个机器人，机器人当前有一个空字符串 t 。执行以下操作之一，直到 s 和 t 都变成空字符串：

You are given a string s and a robot that currently holds an empty string t. Apply one of the following operations until s and t are both empty:

给你一个字符串 s 。它可能包含任意数量的 '*' 字符。你的任务是删除所有的 '*' 字符。 当字符串还存在至少一个 '*' 字符时，你可以执行以下操作：

You are given a string s. It may contain any number of '*' characters. Your task is to remove all '*' characters. While there is a '*', do the following operation: