blocks|key|2614753|text|返回“特殊值”(如0+)的问题是，数组中的第二大数字可能是0。你怎么能分辨出不同之处呢？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2614754|编写的函数无法使用它的返回值来指示何时发生错误。您可以重构它以返回错误代码并使用out参数来填充找到的值(非常C-样式)，或者您可以抛出一个异常(更多的C%2B%2B样式)。|2614755|编辑：|2614756|我刚刚想到，如果返回的值是数组中第二大数字的索引，则可以使用负数作为“特殊值”。|2614757|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

The problem with returning a 'special value', such as 0, is that the second largest number in the array could be 0. How would you be able to tell the difference?

The function, as written, could not use it's return value to indicate when an error has occured. You could either refactor it to return an error code and use an out parameter to fill out the found value (very C-style), or you could throw an exception (more C++ style).

EDIT:

It just occured to me that if the value returned is the index of the second largest number in the array, you could use negative numbers as 'special values'.

blocks|key|475186|text|面试官给出的功能体是什么？如果没有，我会编写一个函数，返回数组中第二大项的索引。如果没有找到第二大项(就像您的错误案例一样)，我的函数将返回len，以指示没有找到第二大项。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|475187|entityMap^0|1Y|3|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

Is the function body given by the interviewer? If not, I'd write a function that returns the index of the second largest item in the array. If no second largest item is found (like your error cases), my function would return <code>len</code> to indicate that second largest item is not found.

blocks|key|2614773|text|按照标准库模型，在搜索序列时，我们不返回要查找的值，而是将迭代器返回到值(在本例中是指针)。如果我们找不到值，则返回一个迭代器到最后一个元素，签名如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2614774|//+end+is+not+the+last+element,+it+is+one+past+the+last+element
int+*+findSecondLargest(int+*+begin,+int+*+end);|code-block|syntax|javascript|2614775|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Following the standard library model, when searching a sequence, we don't return the value we are looking for, we return an iterator to the value(a pointer in this case). If we don't find the value, we return an iterator to one past the last element, the signature would look like this:

<pre><code>// end is not the last element, it is one past the last element
int * findSecondLargest(int * begin, int * end);
</code></pre>

blocks|key|2614808|text|使用GCC特有的变量数量的args到宏表示法只用于测试，但是无论如何，基本思想是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2614809|如果len小于2时(我认为可以返回一个特殊值，如0或|2614810|+)。|blockquote|2614811|2614812|2614813|2614814|在这里，我返回一个空指针，而不是一个安全的去引用指针，所以在数据中使用0或MinInt没有问题。|unordered-list-item|2614815|2614816|2614817|但是，如果第二大是0。(因为在这种情况下，我无法区分错误和正常返回值。所以我可能会抛出一个异常)|2614818|2614819|2614820|一个合理的输入的例外是相当严重的坏！|2614821|如果数组是{1，1，1}(因为1是最大的数字，而不是第二大的)，则为|2614822|。所以我可能会抛出一个异常)|2614823|2614824|2614825|这是有争议的，但这就是我所建模的行为，也是通过返回NULL。|2614826|所以：|2614827|2614828|differentiate通过使用指针和NULL|2614829|second-largest值从未找到的状态中找到的条件可以通过跟踪最大值来维护，当我们迭代一次|2614830|时|2614831|代码有点费劲，但是FWIW：|2614832|#include+<iostream>

template+<typename+T,+int+N>
T*+second_largest(T+(&arr)[N])
{
++++if+(N+<+2)+return+NULL;
++++T*+largest+=+&arr[0];
++++T*+second+=+NULL;
++++for+(int+i+=+1;+i+<+N;+%2B%2Bi)
++++{
++++++++if+(arr[i]+>+*largest)
++++++++{
++++++++++++second+=+largest;
++++++++++++largest+=+&arr[i];
++++++++}
++++++++else+if+(arr[i]+!=+*largest+&&+(!second+%7C%7C+arr[i]+>+*second))
++++++++++++second+=+&arr[i];
++++++++std::cout+<<+"i+"+<<+i+<<+",+largest+"+<<+(largest+?+*largest+:+-1)
++++++++++++<<+",+second+"+<<+(second+?+*second+:+-1)+<<+'\n';
++++}
++++return+second;
}

#define+TEST(ASSERTION,+ARRAY...)+\
{+\
++++int+x[]+=+{+ARRAY+};+\
++++int*+p+=+second_largest(x);+\
++++assert(ASSERTION);+\
++++std::cout+<<+#ASSERTION+<<+"+passed+for+"+<<+#ARRAY+<<+'\n';+\
}

int+main()
{
++++TEST(*p+==+4,+1,+3,+2,+5,+4,+0);
++++TEST(!p,+1,+1,+1);
++++TEST(!p,+1);
++++TEST(*p+==+1,+1,+2);
++++TEST(*p+==+1,+2,+1);
++++TEST(*p+==+1,+1,+2,+0);
++++std::cout+<<+"all+tests+passed\n";
}|code-block|syntax|javascript|2614833|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1M|8|@]|9|@]|A|$]]|$1|G|3|-4|5|6|7|1N|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|1O|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|1P|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|1Q|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|1R|8|@]|9|@]|A|$]]|$1|N|3|-4|5|6|7|1S|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|1T|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|1U|8|@]|9|@]|A|$]]|$1|R|3|-4|5|6|7|1V|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|1W|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|1X|8|@]|9|@]|A|$]]|$1|W|3|X|5|F|7|1Y|8|@]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1Z|8|@]|9|@]|A|$]]|$1|Z|3|-4|5|6|7|20|8|@]|9|@]|A|$]]|$1|10|3|11|5|6|7|21|8|@]|9|@]|A|$]]|$1|12|3|13|5|6|7|22|8|@]|9|@]|A|$]]|$1|14|3|-4|5|6|7|23|8|@]|9|@]|A|$]]|$1|15|3|16|5|L|7|24|8|@]|9|@]|A|$]]|$1|17|3|18|5|L|7|25|8|@]|9|@]|A|$]]|$1|19|3|1A|5|6|7|26|8|@]|9|@]|A|$]]|$1|1B|3|1C|5|6|7|27|8|@]|9|@]|A|$]]|$1|1D|3|1E|5|1F|7|28|8|@]|9|@]|A|$1G|1H]]|$1|1I|3|-4|5|6|7|29|8|@]|9|@]|A|$]]]|1J|$]]

Uses GCC-specific variable-number-of-args-to-macro notation just for testing, but anyway, basic ideas are:

<blockquote>
 If the len is less than 2 (I think we can return a special value, like 0, or MinInt.)
</blockquote>

<ul>
<li>Here, I return a NULL pointer rather than a safe-to-dereference pointer, so there's no issue with having 0 or MinInt in the data.</li>
</ul>

<blockquote>
 But, if the second largest is 0. (Since in this case, I can not differentiate between an error and a normal return value. so I might throw an exception)
</blockquote>

An exception for a reasonable input is pretty seriously bad!

<blockquote>
 If the array is {1,1,1}(Since 1 is the largest number, not an second largest. so I might throw an exception) 
</blockquote>

This is arguable, but that's the behaviour I've modelled, also by returning NULL.

So:

<ul>
<li>differentiate a found condition from an unfound by using pointers vs NULL</li>
<li>second-largest value can be maintained by tracking largest as we iterate once</li>
</ul>

Code's a bit scrappy, but FWIW:

<pre><code>#include &lt;iostream&gt;

template &lt;typename T, int N&gt;
T* second_largest(T (&amp;arr)[N])
{
 if (N &lt; 2) return NULL;
 T* largest = &amp;arr[0];
 T* second = NULL;
 for (int i = 1; i &lt; N; ++i)
 {
 if (arr[i] &gt; *largest)
 {
 second = largest;
 largest = &amp;arr[i];
 }
 else if (arr[i] != *largest &amp;&amp; (!second || arr[i] &gt; *second))
 second = &amp;arr[i];
 std::cout &lt;&lt; "i " &lt;&lt; i &lt;&lt; ", largest " &lt;&lt; (largest ? *largest : -1)
 &lt;&lt; ", second " &lt;&lt; (second ? *second : -1) &lt;&lt; '\n';
 }
 return second;
}

#define TEST(ASSERTION, ARRAY...) \
{ \
 int x[] = { ARRAY }; \
 int* p = second_largest(x); \
 assert(ASSERTION); \
 std::cout &lt;&lt; #ASSERTION &lt;&lt; " passed for " &lt;&lt; #ARRAY &lt;&lt; '\n'; \
}

int main()
{
 TEST(*p == 4, 1, 3, 2, 5, 4, 0);
 TEST(!p, 1, 1, 1);
 TEST(!p, 1);
 TEST(*p == 1, 1, 2);
 TEST(*p == 1, 2, 1);
 TEST(*p == 1, 1, 2, 0);
 std::cout &lt;&lt; "all tests passed\n";
}
</code></pre>

I just had an interview question about how I design a simple function - find the second largest number in an Int Array.

<pre><code>int findSecondLargest(int * arr, int len){
 int second = 0;
 ...

 return second;
}
</code></pre>

However, I was asked the following questions about how I deal with the issues.

<ol>
<li>If the len is less than 2(I think we can return a special value, like 0, or MinInt.)</li>
<li>But, if the second largest is 0. (Since in this case, I can not differentiate between an error and a normal return value. so I might throw an exception)</li>
<li>If the array is {1,1,1}(Since 1 is the largest number, not an second largest. so I might throw an exception)</li>
</ol>

I really felt confused. I think it is not possible to deal with all situations. We usually have to document the usage of our function, instead of throw exception.

Hope some advice. Thanks

//The function body is written by myself. I really like the design supposed by Donotalo and PigBen

Question about function design

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我刚刚有一个面试问题，问我如何设计一个简单的函数--在Int中找到第二大数字。int findSecondLargest(int * arr, int len){    int second = 0;    ...    return second;}然而，有人问我如何处理这些问题。如果小于2(我认为我们可以返回一个特...

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