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Why doesn't Dijkstra's algorithm work for negative weight edges?
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Recall that in Dijkstra's algorithm, once a vertex is marked as "closed" (and out of the open set) - the algorithm found the shortest path to it, and will never have to develop this node again - it assumes the path developed to this path is the shortest.
But with negative ...
Differences in boolean operators: & vs && and | vs ||
... the rules for && and || but what are & and | ? Please explain these to me with an example.
11 Answers
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What's the difference between lapply and do.call?
...r to map in other languages:
lapply returns a list of the same length as X, each element of which is the result of applying FUN to the corresponding element of X.
do.call constructs and executes a function call from a name or a function and a list of arguments to be passed to it.
Map applies a fun...
How to determine if a number is odd in JavaScript
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Use the bitwise AND operator.
function oddOrEven(x) {
return ( x & 1 ) ? "odd" : "even";
}
function checkNumber(argNumber) {
document.getElementById("result").innerHTML = "Number " + argNumber + " is " + oddOrEven(argNumber);
}
checkNumber(17);
<div i...
Running V8 Javascript Engine Standalone
...shell.
Running the console:
$> ./v8-shell
V8 version 2.0.2
> var x = 10;
> x
10
> function foo(x) { return x * x; }
> foo
function foo(x) { return x * x; }
> quit()
Executing Javascript from the command line:
$> ./v8-shell -e 'print("10*10 = " + 10*10)'
10*10 = 100
Man...
How to filter by IP address in Wireshark?
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Match destination: ip.dst == x.x.x.x
Match source: ip.src == x.x.x.x
Match either: ip.addr == x.x.x.x
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What is an invariant?
The word seems to get used in a number of contexts. The best I can figure is that they mean a variable that can't change. Isn't that what constants/finals (darn you Java!) are for?
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Finding differences between elements of a list
...t izip as zip
def differences(seq):
iterable, copied = tee(seq)
next(copied)
for x, y in zip(iterable, copied):
yield y - x
Or using itertools.islice instead:
from itertools import islice
def differences(seq):
nexts = islice(seq, 1, None)
for x, y in zip(seq, nexts):...
How do I calculate square root in Python?
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sqrt=x**(1/2) is doing integer division. 1/2 == 0.
So you're computing x(1/2) in the first instance, x(0) in the second.
So it's not wrong, it's the right answer to a different question.
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“x not in y” or “not x in y”
...tor, which could be applied to a in b just as easily as any other boolean expression, whereas not in was a separate operator for convenience and clarity.
The disassembly above was revealing! It seems that while not obviously is a logical negation operator, the form not a in b is special cased so th...