《左耳听风》-ARTS-打卡记录-第八周

Algorithm

反转字符串中的元音字符

上一期中发现自己实际上把string赋值的做法是多余的,这里可以考虑在一个string上进行操作.于是修改后的代码如下所示:(注意这里把之前重复判断元音的代码抽象进了方法中,这个对时间复杂度降低没有太多影响的)

class Solution {
public:
    bool isQuilified(char c)
    {
        return ((c=='a') || (c=='e') || (c=='i') || (c=='o') || (c=='u') || (c=='A') || (c=='E') || (c=='I') || (c=='O') || (c=='U'));
    }
    
    string reverseVowels(string s) {
        int i = 0;
        int j = s.size()-1;
        while(i<j)
        {
            if(isQuilified(s[i]))
            {
                if(s[j])
                {
                    swap(s[i], s[j]);
                    i++;
                    j--;
                }
                else
                {
                    j--;
                }
            }
            else
            {
                i++;
            }

        }
        return s;
    }
};

后来查看了那些执行时间短的提交代码,发现他们把if的嵌套结构改为了并列的if结构.这样确实效率提升了--因为执行的语句减少了.

class Solution {
public:

    bool isQuilified(char c)
    {
        return ((c=='a') || (c=='e') || (c=='i') || (c=='o') || (c=='u') || (c=='A') || (c=='E') || (c=='I') || (c=='O') || (c=='U'));
    }
    string reverseVowels(string s) {
        int i = 0;
        int j = s.size()-1;
        while(i<j)
        {
            if(!isQuilified(s[i]))
            {
               i++;
               continue; 
            }
                
            if(isQuilified(s[j]))
            {
                swap(s[i], s[j]);
                i++;
                j--;
            }
            else
            {
                j--;
            }
        }
        return s;
    }
};

Review

How To Ask Questions The Smart Way(2/8)

Before You Ask

Before asking a technical question by e-mail, or in a newsgroup, or on a website chat board, do the following:

Try to find an answer by searching the archives of the forum or mailing list you plan to post to.
Try to find an answer by searching the Web.
Try to find an answer by reading the manual.
Try to find an answer by reading a FAQ.
Try to find an answer by inspection or experimentation.
Try to find an answer by asking a skilled friend.
If you're a programmer, try to find an answer by reading the source code.

When you ask your question, display the fact that you have done these things first; this will help establish that you're not being a lazy sponge and wasting people's time. Better yet, display what you have learned from doing these things. We like answering questions for people who have demonstrated they can learn from the answers.

Use tactics like doing a Google search on the text of whatever error message you get (searching Google groups as well as Web pages). This might well take you straight to fix documentation or a mailing list thread answering your question. Even if it doesn't, saying “I googled on the following phrase but didn't get anything that looked promising” is a good thing to do in e-mail or news postings requesting help, if only because it records what searches won't help. It will also help to direct other people with similar problems to your thread by linking the search terms to what will hopefully be your problem and resolution thread.

Take your time. Do not expect to be able to solve a complicated problem with a few seconds of Googling. Read and understand the FAQs, sit back, relax and give the problem some thought before approaching experts. Trust us, they will be able to tell from your questions how much reading and thinking you did, and will be more willing to help if you come prepared. Don't instantly fire your whole arsenal of questions just because your first search turned up no answers (or too many).

Prepare your question. Think it through. Hasty-sounding questions get hasty answers, or none at all. The more you do to demonstrate that having put thought and effort into solving your problem before seeking help, the more likely you are to actually get help.

Beware of asking the wrong question. If you ask one that is based on faulty assumptions, J. Random Hacker is quite likely to reply with a uselessly literal answer while thinking “Stupid question...”, and hoping the experience of getting what you asked for rather than what you needed will teach you a lesson.

Never assume you are entitled to an answer. You are not; you aren't, after all, paying for the service. You will earn an answer, if you earn it, by asking a substantial, interesting, and thought-provoking question — one that implicitly contributes to the experience of the community rather than merely passively demanding knowledge from others.

On the other hand, making it clear that you are able and willing to help in the process of developing the solution is a very good start. “Would someone provide a pointer?”, “What is my example missing?”, and “What site should I have checked?” are more likely to get answered than “Please post the exact procedure I should use.” because you're making it clear that you're truly willing to complete the process if someone can just point you in the right direction.

When You Ask

Choose your forum carefully

Be sensitive in choosing where you ask your question. You are likely to be ignored, or written off as a loser, if you:

post your question to a forum where it's off topic
post a very elementary question to a forum where advanced technical questions are expected, or vice-versa
cross-post to too many different newsgroups
post a personal e-mail to somebody who is neither an acquaintance of yours nor personally responsible for solving your problem

Hackers blow off questions that are inappropriately targeted in order to try to protect their communications channels from being drowned in irrelevance. You don't want this to happen to you.

The first step, therefore, is to find the right forum. Again, Google and other Web-searching methods are your friend. Use them to find the project webpage most closely associated with the hardware or software giving you difficulties. Usually it will have links to a FAQ (Frequently Asked Questions) list, and to project mailing lists and their archives. These mailing lists are the final places to go for help, if your own efforts (including reading those FAQs you found) do not find you a solution. The project page may also describe a bug-reporting procedure, or have a link to one; if so, follow it.

Shooting off an e-mail to a person or forum which you are not familiar with is risky at best. For example, do not assume that the author of an informative webpage wants to be your free consultant. Do not make optimistic guesses about whether your question will be welcome — if you're unsure, send it elsewhere, or refrain from sending it at all.

When selecting a Web forum, newsgroup or mailing list, don't trust the name by itself too far; look for a FAQ or charter to verify your question is on-topic. Read some of the back traffic before posting so you'll get a feel for how things are done there. In fact, it's a very good idea to do a keyword search for words relating to your problem on the newsgroup or mailing list archives before you post. It may find you an answer, and if not it will help you formulate a better question.

Don't shotgun-blast all the available help channels at once, that's like yelling and irritates people. Step through them softly.

Know what your topic is! One of the classic mistakes is asking questions about the Unix or Windows programming interface in a forum devoted to a language or library or tool portable across both. If you don't understand why this is a blunder, you'd be best off not asking any questions at all until you get it.

In general, questions to a well-selected public forum are more likely to get useful answers than equivalent questions to a private one. There are multiple reasons for this. One is simply the size of the pool of potential respondents. Another is the size of the audience; hackers would rather answer questions that educate many people than questions serving only a few.

Understandably, skilled hackers and authors of popular software are already receiving more than their fair share of mis-targeted messages. By adding to the flood, you could in extreme cases even be the straw that breaks the camel's back — quite a few times, contributors to popular projects have withdrawn their support because collateral damage in the form of useless e-mail traffic to their personal accounts became unbearable.

在提问之前

在你准备要通过电子邮件、新闻群组或者聊天室提出技术问题前，请先做到以下事情：

尝试在你准备提问的论坛的旧文章中搜索答案。
尝试上网搜索以找到答案。
尝试阅读手册以找到答案。
尝试阅读常见问题文件（FAQ）以找到答案。
尝试自己检查或试验以找到答案
向你身边的强者朋友打听以找到答案。
如果你是程序开发者，请尝试阅读源代码以找到答案

当你提出问题的时候，请先表明你已经做了上述的努力；这将有助于树立你并不是一个不劳而获且浪费别人的时间的提问者。如果你能一并表达在做了上述努力的过程中所**学到**的东西会更好，因为我们更乐于回答那些表现出能从答案中学习的人的问题。

运用某些策略，比如先用Google搜索你所遇到的各种错误信息（既搜索Google论坛，也搜索网页），这样很可能直接就找到了能解决问题的文件或邮件列表线索。即使没有结果，在邮件列表或新闻组寻求帮助时加上一句 我在Google中搜过下列句子但没有找到什么有用的东西 也是件好事，即使它只是表明了搜索引擎不能提供哪些帮助。这么做（加上搜索过的字串）也让遇到相似问题的其他人能被搜索引擎引导到你的提问来。

别着急，不要指望几秒钟的Google搜索就能解决一个复杂的问题。在向专家求助之前，再阅读一下常见问题文件（FAQ）、放轻松、坐舒服一些，再花点时间思考一下这个问题。相信我们，他们能从你的提问看出你做了多少阅读与思考，如果你是有备而来，将更有可能得到解答。不要将所有问题一股脑拋出，只因你的第一次搜索没有找到答案（或者找到太多答案）。

准备好你的问题，再将问题仔细的思考过一遍，因为草率的发问只能得到草率的回答，或者根本得不到任何答案。越是能表现出在寻求帮助前你为解决问题所付出的努力，你越有可能得到实质性的帮助。

小心别问错了问题。如果你的问题基于错误的假设，某个普通黑客（J. Random Hacker）多半会一边在心里想着蠢问题…，一边用无意义的字面解释来答复你，希望着你会从问题的回答（而非你想得到的答案）中汲取教训。

绝不要自以为**够格得到答案，你没有；你并没有。毕竟你没有为这种服务支付任何报酬。你将会是自己去挣到**一个答案，靠提出有内涵的、有趣的、有思维激励作用的问题 --一个有潜力能贡献社区经验的问题，而不仅仅是被动的从他人处索取知识。

另一方面，表明你愿意在找答案的过程中做点什么是一个非常好的开端。谁能给点提示？、我的这个例子里缺了什么？以及我应该检查什么地方比请把我需要的确切的过程贴出来更容易得到答复。因为你表现出只要有人能指个正确方向，你就有完成它的能力和决心。

当你提问时

慎选提问的论坛

小心选择你要提问的场合。如果你做了下述的事情，你很可能被忽略掉或者被看作失败者：

在与主题不合的论坛上贴出你的问题
在探讨进阶技术问题的论坛张贴非常初级的问题；反之亦然
在太多的不同新闻群组上重复转贴同样的问题（cross-post）
向既非熟人也没有义务解决你问题的人发送私人电邮

黑客会剔除掉那些搞错场合的问题，以保护他们沟通的渠道不被无关的东西淹没。你不会想让这种事发生在自己身上的。

因此，第一步是找到对的论坛。再说一次，Google和其它搜索引擎还是你的朋友，用它们来找到与你遭遇到困难的软硬件问题最相关的网站。通常那儿都有常见问题（FAQ）、邮件列表及相关说明文件的链接。如果你的努力（包括**阅读**FAQ）都没有结果，网站上也许还有报告Bug（Bug-reporting）的流程或链接，如果是这样，连过去看看。

向陌生的人或论坛发送邮件最可能是风险最大的事情。举例来说，别假设一个提供丰富内容的网页的作者会想充当你的免费顾问。不要对你的问题是否会受到欢迎做太乐观的估计 -- 如果你不确定，那就向别处发送，或者压根别发。

在选择论坛、新闻群组或邮件列表时，别太相信名字，先看看FAQ或者许可书以弄清楚你的问题是否切题。发文前先翻翻已有的话题，这样可以让你感受一下那里的文化。事实上，事先在新闻组或邮件列表的历史记录中搜索与你问题相关的关键词是个极好的主意，也许这样就找到答案了。即使没有，也能帮助你归纳出更好的问题。

别像机关枪似的一次"扫射"所有的帮助渠道，这就像大喊大叫一样会使人不快。要一个一个地来。

搞清楚你的主题！最典型的错误之一是在某种致力于跨平台可移植的语言、套件或工具的论坛中提关于Unix或Windows操作系统程序界面的问题。如果你不明白为什么这是大错，最好在搞清楚这之间差异之前什么也别问。

一般来说，在仔细挑选的公共论坛中提问，会比在私有论坛中提同样的问题更容易得到有用的回答。有几个理由可以支持这点，一是看潜在的回复者有多少，二是看观众有多少。黑客较愿意回答那些能帮助到许多人的问题。

可以理解的是，老练的黑客和一些热门软件的作者正在接受过多的错发信息。就像那根最后压垮骆驼背的稻草一样，你的加入也有可能使情况走向极端 -- 已经好几次了，一些热门软件的作者从自己软件的支持中抽身出来，因为伴随而来涌入其私人邮箱的无用邮件变得无法忍受。

Tips

1.在备战软考时,可以把官方的教程作为字典来使用,而把真题作为主食来食用,这样就能够有针对性地,比较高效地来复习.

What is different between dynamic_cast and qobject_cast