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Why do we check up to the square root of a prime number to determine if it is prime?
... is not a prime, it can be factored into two factors a and b:
n = a * b
Now a and b can't be both greater than the square root of n, since then the product a * b would be greater than sqrt(n) * sqrt(n) = n. So in any factorization of n, at least one of the factors must be smaller than the square ...
What's a good rate limiting algorithm?
... = 8.0; // unit: seconds
allowance = rate; // unit: messages
last_check = now(); // floating-point, e.g. usec accuracy. Unit: seconds
when (message_received):
current = now();
time_passed = current - last_check;
last_check = current;
allowance += time_passed * (rate / per);
if (allowance...
Format Instant to String
...tant a time-zone is required. Without a time-zone, the formatter does not know how to convert the instant to human date-time fields, and therefore throws an exception.
The time-zone can be added directly to the formatter using withZone().
DateTimeFormatter formatter =
DateTimeFormatter.ofLocal...
Explain ExtJS 4 event handling
...k event handler.
Let's retrieve Element:
var el = Ext.get('test_node');
Now let's check docs for click event. It's handler may have three parameters:
click( Ext.EventObject e, HTMLElement t, Object eOpts )
Knowing all this stuff we can assign handler:
// event name event handler...
What is memory fragmentation?
...---
| |
----------------------------------
Now, allocate some of it (5 allocations):
----------------------------------
|aaaabbccccccddeeee |
----------------------------------
Now, free the first four allocations but not the fifth:
---------------------...
I lost my .keystore file?
...
Now it is possible don't worry, here is the full and final steps to reset .JKS file.
Step-1
Download the UPLOAD CERTIFICATE (file name - upload_cert.der) from your Google Play Store Console
Step-2
Go to this LINK http...
PHP calculate age
...:createFromFormat('d/m/Y', '12/02/1973', $tz)
->diff(new DateTime('now', $tz))
->y;
As of PHP 5.3.0 you can use the handy DateTime::createFromFormat to ensure that your date does not get mistaken for m/d/Y format and the DateInterval class (via DateTime::diff) to get the number of ...
Memoization in Haskell?
...u can check the work so far by verifying that toList nats gives you [0..]
Now,
f_tree :: Tree Int
f_tree = fmap (f fastest_f) nats
fastest_f :: Int -> Int
fastest_f = index f_tree
works just like with list above, but instead of taking linear time to find each node, can chase it down in loga...
How to round the minute of a datetime object
...ect to any time lapse in seconds
dt : datetime.datetime object, default now.
roundTo : Closest number of seconds to round to, default 1 minute.
Author: Thierry Husson 2012 - Use it as you want but don't blame me.
"""
if dt == None : dt = datetime.datetime.now()
seconds = (dt.replac...
Ukkonen's suffix tree algorithm in plain English
...e an initial tree, which looks like this:
And what it means is this:
Now we progress to position 2 (right after b). Our goal at each step
is to insert all suffixes up to the current position. We do this
by
expanding the existing a-edge to ab
inserting one new edge for b
In our representati...