Here is a piece of C++ code that shows some very peculiar behavior. For some strange reason, sorting the data (*before* the timed region) miraculously makes the loop almost six times faster.

```c++
#include &lt;algorithm&gt;
#include &lt;ctime&gt;
#include &lt;iostream&gt;

int main()
{
	// Generate data
	const unsigned arraySize = 32768;
	int data[arraySize];

	for (unsigned c = 0; c &lt; arraySize; ++c)
		data[c] = std::rand() % 256;

	// !!! With this, the next loop runs faster.
	std::sort(data, data + arraySize);

	// Test
	clock_t start = clock();
	long long sum = 0;
	for (unsigned i = 0; i &lt; 100000; ++i)
	{
		for (unsigned c = 0; c &lt; arraySize; ++c)
		{	// Primary loop
			if (data[c] &gt;= 128)
				sum += data[c];
		}
	}

	double elapsedTime = static_cast&lt;double&gt;(clock()-start) / CLOCKS_PER_SEC;

	std::cout &lt;&lt; elapsedTime &lt;&lt; &#39;\n&#39;;
    std::cout &lt;&lt; &quot;sum = &quot; &lt;&lt; sum &lt;&lt; &#39;\n&#39;;
}
```

- Without `std::sort(data, data + arraySize);`, the code runs in 11.54 seconds.
- With the sorted data, the code runs in 1.93 seconds.


(Sorting itself takes more time than this one pass over the array, so it&#39;s not actually worth doing if we needed to calculate this for an unknown array.)

---

Initially, I thought this might be just a language or compiler anomaly, so I tried Java:

```java
import java.util.Arrays;
import java.util.Random;

public class Main
{
	public static void main(String[] args)
	{
		// Generate data
		int arraySize = 32768;
		int data[] = new int[arraySize];

		Random rnd = new Random(0);
		for (int c = 0; c &lt; arraySize; ++c)
		    data[c] = rnd.nextInt() % 256;

		// !!! With this, the next loop runs faster
		Arrays.sort(data);

		// Test
		long start = System.nanoTime();
		long sum = 0;
		for (int i = 0; i &lt; 100000; ++i)
		{
			for (int c = 0; c &lt; arraySize; ++c)
			{  	// Primary loop
				if (data[c] &gt;= 128)
					sum += data[c];
			}
		}

		System.out.println((System.nanoTime() - start) / 1000000000.0);
		System.out.println(&quot;sum = &quot; + sum);
	}
}
```

With a similar but less extreme result.

---

My first thought was that sorting brings the data into the [cache](https://en.wikipedia.org/wiki/CPU_cache), but then I thought how silly that was because the array was just generated.

- What is going on?
- Why is processing a sorted array faster than processing an unsorted array?

The code is summing up some independent terms, so the order should not matter.

---

**Related / followup Q&amp;As** about the same effect with different / later compilers and options:

* https://stackoverflow.com/q/66521344
* https://stackoverflow.com/q/28875325

Why is processing a sorted array faster than processing an unsorted array?

I accidentally **committed the wrong files** to [Git][1] but didn&#39;t push the commit to the server yet.

How can I **undo those commits from the local repository**?

The only way seems to be to copy the edits in some kind of GUI text editor, then wipe the whole local clone, then re-clone the repository, then re-applying the edits. However,
 - This can cause data loss.
 - It&#39;s very hard to do this when only an accidental `git commit` was run.

Is there a better way?

  [1]: https://en.wikipedia.org/wiki/Git

How do I undo the most recent local commits in Git?

I want to delete a branch both locally and remotely.
### Failed Attempts to Delete a Remote Branch

```bash
$ git branch -d remotes/origin/bugfix
error: branch &#39;remotes/origin/bugfix&#39; not found.

$ git branch -d origin/bugfix
error: branch &#39;origin/bugfix&#39; not found.

$ git branch -rd origin/bugfix
Deleted remote branch origin/bugfix (was 2a14ef7).

$ git push
Everything up-to-date

$ git pull
From github.com:gituser/gitproject

* [new branch] bugfix -&gt; origin/bugfix
Already up-to-date.
```

What should I do differently to successfully delete the `remotes/origin/bugfix` branch both locally and remotely?


How do I delete a Git branch locally and remotely?

What are the differences between `git pull` and `git fetch`?

What is the difference between &#39;git pull&#39; and &#39;git fetch&#39;?

What is the use of the `yield` keyword in Python? What does it do?

For example, I&#39;m trying to understand this code&lt;sup&gt;**1**&lt;/sup&gt;:

    def _get_child_candidates(self, distance, min_dist, max_dist):
        if self._leftchild and distance - max_dist &lt; self._median:
            yield self._leftchild
        if self._rightchild and distance + max_dist &gt;= self._median:
            yield self._rightchild	

And this is the caller:

    result, candidates = [], [self]
    while candidates:
        node = candidates.pop()
        distance = node._get_dist(obj)
        if distance &lt;= max_dist and distance &gt;= min_dist:
            result.extend(node._values)
        candidates.extend(node._get_child_candidates(distance, min_dist, max_dist))
    return result

What happens when the method `_get_child_candidates` is called?
Is a list returned? A single element? Is it called again? When will subsequent calls stop?


----------


&lt;sub&gt;
1. This piece of code was written by Jochen Schulz (jrschulz), who made a great Python library for metric spaces. This is the link to the complete source: &lt;a href=&quot;https://well-adjusted.de/~jrspieker/mspace/&quot;&gt;Module mspace&lt;/a&gt;.&lt;/sub&gt; 

What does the &quot;yield&quot; keyword do?

I&#39;ve been messing around with [JSON][1] for some time, just pushing it out as text and it hasn&#39;t hurt anybody (that I know of), but I&#39;d like to start doing things properly.

I have seen *so* many purported &quot;standards&quot; for the JSON content type:

```lang-none
application/json
application/x-javascript
text/javascript
text/x-javascript
text/x-json
```

But which one is correct, or best? I gather that there are security and browser support issues varying between them.

I know there&#39;s a similar question, *[What MIME type if JSON is being returned by a REST API?][2]*, but I&#39;d like a slightly more targeted answer.

  [1]: http://en.wikipedia.org/wiki/JSON
  [2]: https://stackoverflow.com/questions/404470/what-mime-type-if-json-is-being-returned-by-a-rest-api


What is the correct JSON content type?

How do I remove a specific value from an array? Something like:

```javascript
array.remove(value);  // removes all elements with value
```

I have to use *core* JavaScript. Frameworks are not allowed.


How can I remove a specific item from an array?

I mistakenly added files to Git using the command:

    git add myfile.txt

I have not yet run `git commit`. Is there a way to undo this, so these files won&#39;t be included in the commit?



How do I undo &#39;git add&#39; before commit?

I don&#39;t want to rename a remote branch, as described in *https://stackoverflow.com/questions/1526794/rename-master-branch-for-both-local-and-remote-git-repositories?answertab=votes#tab-top*.

How can I rename a local branch which hasn&#39;t been pushed to a remote repository?

In case you need to rename a **remote** branch as well:  
*https://stackoverflow.com/questions/30590083/how-to-rename-a-remote-git-branch-name/30590238#30590238*

  [1]: https://stackoverflow.com/questions/1526794/git-rename-remote-branch



How do I rename a local Git branch?

After reading [Hidden Features and Dark Corners of C++/STL][1] on `comp.lang.c++.moderated`, I was completely surprised that the following snippet compiled and worked in both Visual Studio 2008 and G++ 4.4.

Here&#39;s the code:

    #include &lt;stdio.h&gt;
    int main()
    {
        int x = 10;
        while (x --&gt; 0) // x goes to 0
        {
            printf(&quot;%d &quot;, x);
        }
    }

Output:

    9 8 7 6 5 4 3 2 1 0

I&#39;d assume this is C, since it works in GCC as well. Where is this defined in the standard, and where has it come from?

  [1]: http://groups.google.com/group/comp.lang.c++.moderated/msg/33f173780d58dd20

What is the &quot;--&gt;&quot; operator in C/C++?

Programming language books explain that value types are created on the **stack**, and reference types are created on the **heap**, without explaining what these two things are. I haven&#39;t read a clear explanation of this.  I understand what _a stack_ is. But, 

* Where and what are they (physically in a real computer&#39;s memory)?
* To what extent are they controlled by the OS or language run-time?
* What is their scope?
* What determines the size of each of them?
* What makes one faster? 


  [1]: http://stackoverflow.com/questions/655308/what-is-the-difference-between-the-stack-and-heap-data-structures

What and where are the stack and heap?

Can I use comments inside a JSON file? If so, how?

Can comments be used in JSON?

How do I force an overwrite of local files on a `git pull`?

**The scenario is the following:**

- A team member is modifying the templates for a website we are working on
- They are adding some images to the images directory (but forgets to add them under source control)
- They are sending the images by mail, later, to me
- I&#39;m adding the images under the source control and pushing them to GitHub together with other changes
- They cannot pull updates from GitHub because Git doesn&#39;t want to overwrite their files.

**This is the error I&#39;m getting:**

&gt; error: Untracked working tree file &#39;public/images/icon.gif&#39; would be overwritten by merge

How do I force Git to overwrite them? The person is a designer - usually, I resolve all the conflicts by hand, so the server has the most recent version that they just need to update on their computer.

  [1]: http://en.wikipedia.org/wiki/Git_%28software%29


How do I force &quot;git pull&quot; to overwrite local files?

Why do certain random strings produce colors when entered as background colors in HTML?

For example, the following code produces a page with a **red background** across all browsers and platforms:

&lt;!-- begin snippet: js hide: false --&gt;

&lt;!-- language: lang-html --&gt;

    &lt;body bgcolor=&quot;chucknorris&quot;&gt; test &lt;/body&gt;

&lt;!-- end snippet --&gt;

On the other hand, the value `chucknorr` produces a **yellow background**!

What’s going on here?

Why does HTML think “chucknorris” is a color?

Is it possible to toggle the visibility of an element, using the functions `.hide()`, `.show()` or `.toggle()`?

How would you test if an element is `visible` or `hidden`?


How do I check if an element is hidden in jQuery?

Recently, I ran some of my JavaScript code through Crockford&#39;s [JSLint][1], and it gave the following error:

&gt; Problem at line 1 character 1: Missing &quot;use strict&quot; statement.

Doing some searching, I realized that some people add `&quot;use strict&quot;;` into their JavaScript code. Once I added the statement, the error stopped appearing. Unfortunately, Google did not reveal much of the history behind this string statement. Certainly it must have something to do with how the JavaScript is interpreted by the browser, but I have no idea what the effect would be.

So what is `&quot;use strict&quot;;` all about, what does it imply, and is it still relevant?

Do any of the current browsers respond to the `&quot;use strict&quot;;` string or is it for future use?

  [1]: http://www.jslint.com/

What does &quot;use strict&quot; do in JavaScript, and what is the reasoning behind it?

Somebody pushed a branch called `test` with `git push origin test` to a shared repository. I can see the branch with `git branch -r`.

How do I check out the remote `test` branch? I&#39;ve tried:

 - `git checkout test`, which does nothing
 - `git checkout origin/test` gives `* (no branch)`




How do I check out a remote Git branch?

How can I redirect the user from one page to another using jQuery or pure JavaScript?


How do I redirect to another webpage?

I wrote the wrong thing in a commit message.

How can I change the message? The commit has not been pushed yet.

How to modify existing, unpushed commit messages?

How do you delete untracked local files from your current working tree?



How to remove local (untracked) files from the current Git working tree

How would you explain JavaScript closures to someone with a knowledge of the concepts they consist of (for example functions, variables and the like), but does not understand closures themselves?

I have seen [the Scheme example][1] given on Wikipedia, but unfortunately it did not help.

  [1]: http://en.wikipedia.org/wiki/Scheme_%28programming_language%29


How do JavaScript closures work?

How do I revert from my current state to a snapshot made on a certain commit?

If I do `git log`, then I get the following output:

    $ git log
    commit a867b4af366350be2e7c21b8de9cc6504678a61b`
    Author: Me &lt;me@me.com&gt;
    Date:   Thu Nov 4 18:59:41 2010 -0400

    blah blah blah...

    commit 25eee4caef46ae64aa08e8ab3f988bc917ee1ce4
    Author: Me &lt;me@me.com&gt;
    Date:   Thu Nov 4 05:13:39 2010 -0400

    more blah blah blah...

    commit 0766c053c0ea2035e90f504928f8df3c9363b8bd
    Author: Me &lt;me@me.com&gt;
    Date:   Thu Nov 4 00:55:06 2010 -0400

    And yet more blah blah...

    commit 0d1d7fc32e5a947fbd92ee598033d85bfc445a50
    Author: Me &lt;me@me.com&gt;
    Date:   Wed Nov 3 23:56:08 2010 -0400

    Yep, more blah blah.

How do I revert to the commit from November 3, i.e. commit `0d1d7fc`?


How do I revert a Git repository to a previous commit?

What does this do?

    if __name__ == &quot;__main__&quot;:
        print(&quot;Hello world!&quot;)


What does if __name__ == &quot;__main__&quot;: do?

I&#39;ve recently started maintaining someone else&#39;s JavaScript code. I&#39;m fixing bugs, adding features and also trying to tidy up the code and make it more consistent.

The previous developer used two ways of declaring functions and I can&#39;t work out if there is a reason behind it or not.

The two ways are:

    var functionOne = function() {
        // Some code
    };

&lt;!-- --&gt;

    function functionTwo() {
        // Some code
    }

What are the reasons for using these two different methods and what are the pros and cons of each? Is there anything that can be done with one method that can&#39;t be done with the other?


var functionName = function() {} vs function functionName() {}

Usually I would expect a `String.contains()` method, but there doesn&#39;t seem to be one. 

What is a reasonable way to check for this?


How to check whether a string contains a substring in JavaScript?

I always thought Java uses **pass-by-reference**.

However, I&#39;ve seen [a blog post][1] that claims that Java uses **pass-by-value**.

I don&#39;t think I understand the distinction they&#39;re making.

What is the explanation?

  [1]: http://javadude.com/articles/passbyvalue.htm


Is Java &quot;pass-by-reference&quot; or &quot;pass-by-value&quot;?

If I run the following program, which parses two date strings referencing times 1 second apart and compares them:

	public static void main(String[] args) throws ParseException {
		SimpleDateFormat sf = new SimpleDateFormat(&quot;yyyy-MM-dd HH:mm:ss&quot;);  
		String str3 = &quot;1927-12-31 23:54:07&quot;;  
		String str4 = &quot;1927-12-31 23:54:08&quot;;  
		Date sDt3 = sf.parse(str3);  
		Date sDt4 = sf.parse(str4);  
		long ld3 = sDt3.getTime() /1000;  
		long ld4 = sDt4.getTime() /1000;
		System.out.println(ld4-ld3);
	}

**The output is:**

    353

Why is `ld4-ld3`, not `1` (as I would expect from the one-second difference in the times), but `353`?

If I change the dates to times 1 second later:

    String str3 = &quot;1927-12-31 23:54:08&quot;;  
    String str4 = &quot;1927-12-31 23:54:09&quot;;  

Then `ld4-ld3` will be `1`.

----------

**Java version:**

&lt;!-- language: lang-none --&gt;

    java version &quot;1.6.0_22&quot;
    Java(TM) SE Runtime Environment (build 1.6.0_22-b04)
    Dynamic Code Evolution Client VM (build 0.2-b02-internal, 19.0-b04-internal, mixed mode)

```java
Timezone(`TimeZone.getDefault()`):

sun.util.calendar.ZoneInfo[id=&quot;Asia/Shanghai&quot;,
offset=28800000,dstSavings=0,
useDaylight=false,
transitions=19,
lastRule=null]

Locale(Locale.getDefault()): zh_CN
```

Why is subtracting these two times (in 1927) giving a strange result?

If Python doesn&#39;t have a [ternary conditional operator][1], is it possible to use other language constructs to simulate one?

  [1]: https://en.wikipedia.org/wiki/%3F:#Python

Does Python have a ternary conditional operator?

Example (_note the case_):

&lt;!-- language: lang-cs --&gt;

    string s = &quot;Hello world!&quot;;
    String s = &quot;Hello world!&quot;;

What are the guidelines for the use of each? And what are the differences?

What is the difference between String and string in C#?

There is a file that was being tracked by Git, but now the file is on the `.gitignore` list.

However, that file keeps showing up in `git status` after it&#39;s edited. How do you force Git to completely forget about it?




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