What is the maximum space for Deterministic Turning Machine?
What will be the maximum space for a deterministic Turing machine if its language is decidable in f(n) steps?
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RegEx to capture text between two delimiter characters including 'shared'
If I have the following text...
The quick :brown:fox: jumped over the lazy :dog:.
I would like a regular expression to capture all the words that are between 2
:
characters. In the above example it should return:brown:
,:fox:
,:dog:
.So far, I have this
(\:{1}.\w*\s*\:{1})
which returns:brown:
and:dog:
. I can't quite figure out how to share the:
between the 2 matching groups so that it will also return':fox:'
. 
Exclude particular number regex
I have written a regex to exclude particular numbers 00, 000, and 255
I'm using regex 
^((?!25500000)[19]*)$
The problem I'm facing is when i enter
80
or any other number ending with0
it excludes that number also which i don't want 
Silly regexp URL matching
So I want this:
/services/auth/token
To match this:
http://localhost:3000/services/auth/token/
trailing / optionalbut not this:
http://localhost:3000/services/auth/token/refresh
I'm normally better at this stuff but I'm kind of sleepy. Help SO!!!

Describing the language generated by a context free grammar
Let G= ({S,A,B,C,D,E,Z},(0,1),R,S)
S→EZ E→AC A→01B0Ae B→1B10A; C→10D1Ce D→01C0D Z→0Z1e (e is the empty string)
What is the language described by the CFG? I've had some trouble trying to think of anything.

How does hashing a stream of values guarantees randomness in hyperloglog?
From this stackoverflow post
The main trick behind this algorithm is that if you, observing a stream of random integers, see an integer which binary representation starts with some known prefix, there is a higher chance that the cardinality of the stream is 2^(size of the prefix).
Hyperloglog uses hash to achieve randomness, but how does one prove that hashing a value give random output? Or even more strictly does hash guarantees pseudo random like uniform output?
If hash does not guarantee uniform output, is there a way we can upperbound and quantize the nonuniformity of a hash function?

Problem with the word 'machine' in the definition of machine learning by Mitchell
The definition : A computer program is said to learn from experience E with respect to some class of tasks T and performance measure P, if its performance at tasks in T, as measured by P, improves with experience E.
Here, we talk about what it means for a program to learn rather than a machine, and a program and a machine aren't equivalent so how do we justify calling it 'machine' learning?
I have gone through similar questions ex: What is machine learning? but it doesn't address this aspect.

Is it TRUE that L^R = L, if and only if L is the language of palindromes?
S1: LR = L, if and only if L is the language of palindromes. where LR is obtained by reversing all the strings of L.
Is S1 TRUE?

Regex  Containing "bbb"
I'm trying to create a Regex with chars 'a' and 'b'. The only rule is that the regex must contain the word 'bbb' somewhere.
These are possible: aabbbaaaaaababa, abbba, bbb, aabbbaa, abbabbba, ... These are not possible: abba, a, abb, bba, abbaaaabbaaaabba, ...
I have no idea how can I can express that.
Any ideas? Thanks in Advance!

Theory of automata
Theory of automata is study of abstract machines, like Turing Machines, Finite State Machines, Push Down Automata, Mealy and Moore Machines. discuss and explain which kind of automaton machine promisingly can serve as a recognizer for contextfree languages".