This will run under SpiderMonkey. And with arrow functions introduced in ES6, it's even simpler:. This retrieves array. The optimization is made by caching the value. This is equivalent to a while reverse loop.
It caches the value and is compared to 0, thus faster iteration. For a more complete comparison list, see my JSFiddle. Note: array. I started a JSPerf for array summations. It was quickly constructed and not guaranteed to be complete or accurate, but that's what edit is for :. The fastest loop, according to this test is a while loop in reverse. Based on this test for-vs-forEach-vs-reduce and this loops.
Then comes forEach and reduce which have almost the same performance and varies from browser to browser, but they have the worst performance anyway. It performs faster when I test it on the browser with performance.
Asked 9 years, 6 months ago. Active 4 months ago. Viewed k times. Josh K. Josh K Josh K If you need to see what the fastest way to do something is, try out several, and measure the results. Chad: Well obviously, however I'm not in my "out of the box thinking" days.
I have tried using jslint and other validators online to check if I might have missed something but that doesn't seem to help me find the reason for the code not working either. Is there something that I'm missing above that's preventing the script from executing the addition?? I know this is already solved but I wanted to post a quick ES6 oneliner I wrote after reading this thread and explain it more thoroughly for others who like me don't have a solid math background.
It works because it uses a mathematic formula that Carl Friedrich Gauss came up with. Basically, whenever you are adding the sum of n numbers, you will have pairs in the sequence.
So Gauss figured out that you didn't need to loop through each pair and add them, instead you just need to add the middle pair and multiply that sum by the total number of pairs. This works really well for programming because they aren't looping through each number which in programming would eat through your resources.
You set your placeholder variable equal to one. You also set the number of iterations equal to the input variable. The do loop then adds your placeholder variable with 'i' and then the loop exits when it is no longer greater than 1, which is correct because you have your placeholder equal to one.
While this might not be the most optimal answer for the case of min:0 max:n, it might be the easiest to read and understand. Learn more.
Asked 5 years ago. Active 2 months ago.Help to translate the content of this tutorial to your language!
Recursion is a programming pattern that is useful in situations when a task can be naturally split into several tasks of the same kind, but simpler.
Or when a task can be simplified into an easy action plus a simpler variant of the same task. When a function solves a task, in the process it can call many other functions. A partial case of this is when a function calls itself. In other words, multiplies x by itself n times. So, the recursion reduces a function call to a simpler one, and then — to even more simpler, and so on, until the result becomes obvious.
That limits the application of recursion, but it still remains very wide. There are many tasks where recursive way of thinking gives simpler code, easier to maintain.
The previous one is restored off the top of the stack:. The execution of pow 2, 2 is resumed. As we can see from the illustrations above, recursion depth equals the maximal number of context in the stack. Note the memory requirements.
Contexts take memory.
In our case, raising to the power of n actually requires the memory for n contexts, for all lower values of n. The iterative pow uses a single context changing i and result in the process. Its memory requirements are small, fixed and do not depend on n. Any recursion can be rewritten as a loop. The loop variant usually can be made more effective. And the optimization may be unneeded and totally not worth the efforts. Recursion can give a shorter code, easier to understand and support.
A department may have an array of staff.
For instance, sales department has 2 employees: John and Alice. Or a department may split into subdepartments, like development has two branches: sites and internals. Each of them has their own staff. It is also possible that when a subdepartment grows, it divides into subsubdepartments or teams.
This will run under SpiderMonkey. And with arrow functions introduced in ES6, it's even simpler:. This retrieves array. The optimization is made by caching the value. This is equivalent to a while reverse loop. It caches the value and is compared to 0, thus faster iteration. For a more complete comparison list, see my JSFiddle. Note: array. I started a JSPerf for array summations. It was quickly constructed and not guaranteed to be complete or accurate, but that's what edit is for :.
The fastest loop, according to this test is a while loop in reverse. Based on this test for-vs-forEach-vs-reduce and this loops. Then comes forEach and reduce which have almost the same performance and varies from browser to browser, but they have the worst performance anyway. It performs faster when I test it on the browser with performance.
I think this is a better way. What do you guys think? I tried using performance. I took a very large array and found the sum of all elements of the array. I ran the code three times every time and found forEach and reduce to be a clear winner.
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Division is particularly useful when calculating time, such as finding the number of hours in a quantity of minutes, or when calculating the percent of correct answers completed in a test.
One arithmetic operator that is slightly less familiar is the modulo sometimes known as modulus operator, which calculates the remainder of a quotient after division. As an example, we know that 3 goes into 9 exactly three times, and there is no remainder.
Increment and decrement operators increase or reduce the numerical value of a variable by one. Note that increment and decrement operators can only be used on variables; attempting to use them on a raw number will result in an error.
Increment and decrement operators can be classified as a prefix or postfix operation, depending on whether or not the operator is placed before or after the variable.
In programming, even the humble decimal number system that we all know so well is more complicated than you might think. We use different terms to describe different types of decimal numbers, for example:.
We even have different types of number systems! Decimal is base 10 meaning it uses 0—9 in each columnbut we also have things like:. Before you start to get worried about your brain melting, stop right there!
Returns the remainder left over after you've divided the left number into a number of integer portions equal to the right number. Note : You'll sometimes see numbers involved in arithmetic referred to as operands. Note : You may sometimes see exponents expressed using the older Math.
Let's look at the last example from above, assuming that num2 holds the value 50 and num1 holds the value 10 as originally stated above :.
For example, say you wanted to loop through a list of prices, and add sales tax to each one. You'd use a loop to go through each value in turn and do the necessary calculation for adding the sales tax in each case. The incrementor is used to move to the next value when needed. We've actually provided a simple example showing how this is done — check it out liveand look at the source code to see if you can spot the incrementors!How it works.
Recursion and stack
In other words: Math. If arrow functions scare you, simply remember that the two functions below are the same:. This function is almost identical to the the Minimum value function explained above.
It will accumulate our sum as our function works. The second parameter of the reduce method is the initial value we wish to use.