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Is there any way to use variable itself inside without it's name?
For example, I have a string like this:
someStuffVariableName = "abcdefghijklmnop..."
If I want to manipulate it, I need to write every time name of this var but it's so long:
someStuffVariableName = someStuffVariableName[0:-1]
But,anyway,can I do like this:
someStuffVariableName = self[0:-1] or someStuffVariableName = this.value[0:-1]?
There is not.
Your best options are:
Use a more concise variable name (but don't give up readability!)
Just deal with the length
Note that in some cases, the answer is actually yes. For instance, you can often write x += y instead of x = x + y, and x /= y instead of x = x / y.
But this is for assignment operators only.
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In Python I can do this:
a, b = map(int, input().split(" "))
... to get exactly 2 integers from user input.
How can I achive the exact same result in Rust (get 2 integers as a named tuple) without any extern crates?
For the sheer fun of it, I translated your code as literally as possible to Rust:
// replace with some read from stdin
let input = "1 2";
let (a, b) = if let &[a, b] = &input.split(' ').map(|c| c.parse::<u32>().unwrap()).collect::<Vec<_>>()[..] {
(a, b)
} else {
panic!("ValueError: too many/few values to unpack (expected 2)");
};
println!("a = {}, b = {}", a, b);
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I'm new to Haskell and I'm not sure how to work around the If-Else, for example:
function str = if ((length str) = 2) then (....)
In java we would:
if (str.length =2){
str = "2"}
else { str ="1"}
How do you write it in haskell?
You can use Guards:
fnc :: String -> String
fnc s | length s == 2 = ...
| otherwise = ...
More to Guards
Or conditions
fnc :: String -> String
fnc s = if length s == 2 then ... else ...
It is also possible to use pattern matching, more here.
There are several ways to achieve conditions (e.g. case of) in Haskell.
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I have a data list.
db = [("Ada","works", "IBM")
,("Alice","director", "Ada")
,("Tom","works", "IBM")
,("Tommy","director", "Tom")
,("IBM","isat", "CA")
,("CA","in", "USA")
]
ask db = map (\(x,y,z) -> (z == "IBM")) db
How to calculate the complexity of O(n)？
If I want to get the result by the length of list 2,5,10.O(n) is same like 2,5,10?And If I do
trans2 db = concat (map ((x,y,z) -> concat (map((x',y',z') -> if (z==x') then [] else [(x,y ++ "." ++ y',z')] else []) db)) db )
How can I calculate the O(n)? The runtime of program? The timming complexity
The question is unclear and I expect it will soon be closed. Briefly.
O(n) is a complexity. If you know O(n) and you wanted complexity then you're done.
The length of the list (2, 5, 10, what have you) is not a factor in the complexity in this case since the length is what the n is representing.
There is no code that will calculate the complexity of the algorithm automatically. It is a manual analysis.
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I am new to Haskell and I am trying to turn an int into a reversed digit list(of ints).
What I have is:
Lnat 0 = [0]
Lnat x = [mod x 10] ++ Lnat (div x 10)
However I get the error "Not in scope: data constructor 'Lnat'" on both lines and it crashes trying to load the file.
Could you please explain the root of this and how to fix it?
All values must start with a lowercase character. If it starts with a capital or : then that value is a data constructor, to be used in data declarations. This is what you'll want to change your function to:
lnat 0 = [0]
lnat x = mod x 10 : lnat (div x 10)
Note that I also changed the inefficient ++ operator to : to add a bit more speed.
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In Haskell, how can I create a type to represent a list of length 9 which each elements are an Int between 0 and 9?
You could use smart constructors:
module Sudoku(SudokuSquare, sudokuSquare) where
import Data.Traversable(traverse)
data SudokuSquare = SSquare Int
sudokuSquare :: Int -> Maybe SudokuSquare
sudokuSquare i = if i >= 0 && i <= 9 then Just (SSquare i) else Nothing
buildRow :: [Int] -> Maybe [SudokuSquare]
buildRow = traverse sudokuSquare