I have already seen the community of Crystal, but I couldn't find this problem.
def Twosum(a = [] of Int32, target = 0)
map = {} of Int32 : Int32
a.each_index do |i|
diff = target - a[i]
if map.key?(diff):
return [map.fetch(diff), i]
elsif
map[a[i]] = i
end
end
return 0`enter code here`
end
a = [1,4,6,3]
target = 7
puts(Twosum(a,target))
What's the problem?
Many problems. The one you ask about is: Crystal is very opinionated regarding case. Methods must start with lowercase; yours starts with uppercase, which Crystal does not like at all. Some other problems:
{} of Int32 : Int32 should use a fat arrow, not a colon: {} of Int32 => Int32
if statement does not end with a colon, it is not Python.
There is no method named key?; use has_key?
fetch (in current Crystal version) requires either a block or a second argument that specifies a default; if you do not need to specify a default behaviour (and you don't, since you check whether the key exists), you can just use [].
I'm really not sure what the code is intended to do, so I can't comment on the logic, semantics and style; but here's your code without syntax errors:
def twosum(a = [] of Int32, target = 0)
map = {} of Int32 => Int32
a.each_index do |i|
diff = target - a[i]
if map.has_key?(diff)
return [map[diff], i]
elsif
map[a[i]] = i
end
end
return 0
end
a = [1, 4, 6, 3]
target = 7
puts(twosum(a, target))
Related
I need to create a function that replaces a letter with the letter 13 letters after it in the alphabet (without using encode). I'm relatively new to Python so it has taken me a while to figure out a way to do this without using Encode.
Here's what I have so far. When I use this to type in a normal word like "hello" it works but if I pass through a sentence with special characters I can't figure out how to JUST include letters of the alphabet and skip numbers, spaces or special characters completely.
def rot13(b):
b = b.lower()
a = [chr(i) for i in range(ord('a'),ord('z')+1)]
c = []
d = []
x = a[0:13]
for i in b:
c.append(a.index(i))
for i in c:
if i <= 13:
d.append(a[i::13][1])
elif i > 13:
y = len(a[i:])
z = len(x)- y
d.append(a[z::13][0])
e = ''.join(d)
return e
EDIT
I tried using .isalpha() but this doesn't seem to be working for me - characters are duplicating for some reason when I use it. Is the following format correct:
def rot13(b):
b1 = b.lower()
a = [chr(i) for i in range(ord('a'),ord('z')+1)]
c = []
d = []
x = a[0:13]
for i in b1:
if i.isalpha():
c.append(a.index(i))
for i in c:
if i <= 12:
d.append(a[i::13][1])
elif i > 12:
y = len(a[i:])
z = len(x)- y
d.append(a[z::13][0])
else:
d.append(i)
if message[0].istitle() == True:
d[0] = d[0].upper()
e = ''.join(d)
return e
Following on from comments. OP was advised to use isalpha, and wondering why that's causing duplication (see OP's edit)
This isn't tied to the use of isalpha, it's to do with the second for loop
for i in c:
isn't necessary, and is causing the duplication. You should remove that. Instead you can do the same by just using index = a.index(i). You were already doing this, but for some reason appending to a list instead and causing confusion
Use the index variable any time you would have used i inside the for i in c loop. On a side note, in nested for loops try not to reuse the same variables. It just causes confusion...but that's a matter for code review
Assuming you do all that right it should work.
I am finding some weird behavior when using index.
#Defined in the class's initialize
#my_list = [] of Type
index = #my_list.index { |i| i.value == 2 } # => 0
#my_list[0] # => 2
#my_list[index] # => error
I get the error:
no overload matches 'Array(Type)#[]' with type (Int32 | Nil)
Not sure why index does not work, as index = 0.
EDIT:
More information. If I do this:
if index == nil
#Do something
#error => undefined method '>=' for Nil (compile-time type is (Int32 | Nil))
elsif index >= 0
#Do something else
end
Which I understand. It could be nil, but since I'm already checking to see if it is nil there shouldn't be a problem here. I'm thinking the previous code snippet is running into the same issue.
The problem is that Array#index is nilable; it may not find anything and return nil, hence it returns an Int32|Nil union.
The compiler eventually fails because Array#[] expects an Int32 argument, but we pass it an Int32|Nil. You must take care of this case (to avoid later bugs) by checking if the return value is truthy for example.
As stated by #julien-portalier :
The problem is that Array#index is nilable; it may not find anything in the array and return Nil, hence it returns an (Int32 | Nil) union.
You can use Object#not_nil! to get ride of the Nil type :
#my_list = [2, 4, 6, 8]
index = #my_list.index { |i| i == 6 }.not_nil! # => 2
# compile type of 'index' is Int32
#my_list[0] # => 2
#my_list[index] # => 6
It will make sure the type returned by Array#index is not Nil, if it is, an exception will be raised (see Nil#not_nil!)
And if you need to handle an index error without using exceptions, you can simply check if Array#index failed :
#my_list = [2, 4, 6, 8]
index = #my_list.index { |i| i == 6 } # => 2
# compile-time type of 'index' is (Int32 | Nil)
if index
# In this scope, compile-time type of 'index' is Int32
#my_list[0] # => 2
#my_list[index] # => 6
end
I'm just going to do this:
def get_index(val)
i = 0
while i < #my_list.size
if #my_list[i].value == val
return i
end
i += 1
end
return -1
end
This way only int values will be returned, no nils. It seems to work fine.
better way is to use times method it's more simple and more clear:
def get_index(val)
#my_list.size.times do |i|
return i if #my_list[i] == val
end
-1
end
UPD
or more simple
def get_index(val)
#my_list.index { |value| value == val } || -1
end
My version of RegEx is being greedy and now working as it suppose to. I need extract each message with timestamp and user who created it. Also if user has two or more consecutive messages it should go inside one match / block / group. How to solve it?
https://regex101.com/r/zD5bR6/1
val pattern = "((a\.b|c\.d)\n(.+\n)+)+?".r
for(m <- pattern.findAllIn(str).matchData; e <- m.subgroups) println(e)
UPDATE
ndn solution throws StackOverflowError when executed:
Exception in thread "main" java.lang.StackOverflowError
at java.util.regex.Pattern$GroupTail.match(Pattern.java:4708)
.......
Code:
val pattern = "(?:.+(?:\\Z|\\n))+?(?=\\Z|\\w\\.\\w)".r
val array = (pattern findAllIn str).toArray.reverse foreach{println _}
for(m <- pattern.findAllIn(str).matchData; e <- m.subgroups) println(e)
I don't think a regular expression is the right tool for this job. My solution below uses a (tail) recursive function to loop over the lines, keep the current username and create a Message for every timestamp / message pair.
import java.time.LocalTime
case class Message(user: String, timestamp: LocalTime, message: String)
val Timestamp = """\[(\d{2})\:(\d{2})\:(\d{2})\]""".r
def parseMessages(lines: List[String], usernames: Set[String]) = {
#scala.annotation.tailrec
def go(
lines: List[String], currentUser: Option[String], messages: List[Message]
): List[Message] = lines match {
// no more lines -> return parsed messages
case Nil => messages.reverse
// found a user -> keep as currentUser
case user :: tail if usernames.contains(user) =>
go(tail, Some(user), messages)
// timestamp and message on next line -> create a Message
case Timestamp(h, m, s) :: msg :: tail if currentUser.isDefined =>
val time = LocalTime.of(h.toInt, m.toInt, s.toInt)
val newMsg = Message(currentUser.get, time, msg)
go(tail, currentUser, newMsg :: messages)
// invalid line -> ignore
case _ =>
go(lines.tail, currentUser, messages)
}
go(lines, None, Nil)
}
Which we can use as :
val input = """
a.b
[10:12:03]
you can also get commands
[10:11:26]
from the console
[10:11:21]
can you check if has been resolved
[10:10:47]
ah, okay
c.d
[10:10:39]
anyways startsLevel is still 4
a.b
[10:09:25]
might be a dead end
[10:08:56]
that need to be started early as well
"""
val lines = input.split('\n').toList
val users = Set("a.b", "c.d")
parseMessages(lines, users).foreach(println)
// Message(a.b,10:12:03,you can also get commands)
// Message(a.b,10:11:26,from the console)
// Message(a.b,10:11:21,can you check if has been resolved)
// Message(a.b,10:10:47,ah, okay)
// Message(c.d,10:10:39,anyways startsLevel is still 4)
// Message(a.b,10:09:25,might be a dead end)
// Message(a.b,10:08:56,that need to be started early as well)
The idea is to take as little characters as possible that will be followed by a username or the end of the string:
(?:.+(?:\Z|\n))+?(?=\Z|\w\.\w)
See it in action
I've been taught to program in Java. Lua is new to me and I've tried to do my homework but am not sure what an if statement of the following nature means.
The code is as follows:
local function getMinHeight(self)
local minHeight = 0
for i=1, minimizedLines do
local line = select(9+i, self:GetRegions())
**if(line) then
minHeight = minHeight + line:GetHeight() + 2.5
end**
end
if(minHeight == 0) then
minHeight = select(2, self:GetFont()) + 2.5
end
return minHeight
end
The if statement with the ** before and after is the part I'm not sure about. I don't know what the if statement is checking. If the line is not nil? If the line exists? If what?
In Lua, anything that's not nil or false evaluates to true in a conditional.
If the line is not nil? If the line exists?
Yes to both, because they kinda mean the same thing.
The select function returns a specific argument from it's list of arguments. It's used primarily with ..., but in this case it's being used to select the (i+9)th value returned by self:GetRegions. If there is no such value (for instance, if GetRegions only returns 5 values), then select returns nil.
if(line) is checking to see that it got a value back from select.
if(line) is being used as a shortcut for if(line ~= nil), since nil evaluates to false in a conditional.
It's worth pointing out that this shortcut is not always appropriate. For instance, we can iterate all the values in a table like this:
key, val = next(lookup)
while key do
print(key, val)
key, val = next(lookup, key)
end
However, this will fail if one of the table's keys happens be false:
lookup = {
["fred"] = "Fred Flinstone",
[true] = "True",
[false] = "False",
}
So we have to explicitly check for nil:
key, val = next(lookup)
while key ~= nil do
print(key, val)
key, val = next(lookup, key)
end
As Mud says, in lua anything other than nil and false is considered truthy. So the if above will pass as long as line is not nil or false.
That said, it worries me a bit the way you have phrased the question - "an if with only one argument".
First, it's not called "argument" - it's called expression. And in most languages is always one. In java, for example, you could do something like this:
bool found = false
...
if(found) {
...
}
ifs only care about the final value of the expression; they don't care whether it's a single variable or a more complex construction.
I ve got the following class and I want to write some Spec test cases, but I am really new to it and I don't know how to start. My class do loke like this:
class Board{
val array = Array.fill(7)(Array.fill(6)(None:Option[Coin]))
def move(x:Int, coin:Coin) {
val y = array(x).indexOf(None)
require(y >= 0)
array(x)(y) = Some(coin)
}
def apply(x: Int, y: Int):Option[Coin] =
if (0 <= x && x < 7 && 0 <= y && y < 6) array(x)(y)
else None
def winner: Option[Coin] = winner(Cross).orElse(winner(Naught))
private def winner(coin:Coin):Option[Coin] = {
val rows = (0 until 6).map(y => (0 until 7).map( x => apply(x,y)))
val cols = (0 until 7).map(x => (0 until 6).map( y => apply(x,y)))
val dia1 = (0 until 4).map(x => (0 until 6).map( y => apply(x+y,y)))
val dia2 = (3 until 7).map(x => (0 until 6).map( y => apply(x-y,y)))
val slice = List.fill(4)(Some(coin))
if((rows ++ cols ++ dia1 ++ dia2).exists(_.containsSlice(slice)))
Some(coin)
else None
}
override def toString = {
val string = new StringBuilder
for(y <- 5 to 0 by -1; x <- 0 to 6){
string.append(apply(x, y).getOrElse("_"))
if (x == 6) string.append ("\n")
else string.append("|")
}
string.append("0 1 2 3 4 5 6\n").toString
}
}
Thank you!
I can only second Daniel's suggestion, because you'll end up with a more practical API by using TDD.
I also think that your application could be nicely tested with a mix of specs2 and ScalaCheck. Here the draft of a Specification to get you started:
import org.specs2._
import org.scalacheck.{Arbitrary, Gen}
class TestSpec extends Specification with ScalaCheck { def is =
"moving a coin in a column moves the coin to the nearest empty slot" ! e1^
"a coin wins if" ^
"a row contains 4 consecutive coins" ! e2^
"a column contains 4 consecutive coins" ! e3^
"a diagonal contains 4 consecutive coins" ! e4^
end
def e1 = check { (b: Board, x: Int, c: Coin) =>
try { b.move(x, c) } catch { case e => () }
// either there was a coin before somewhere in that column
// or there is now after the move
(0 until 6).exists(y => b(x, y).isDefined)
}
def e2 = pending
def e3 = pending
def e4 = pending
/**
* Random data for Coins, x position and Board
*/
implicit def arbitraryCoin: Arbitrary[Coin] = Arbitrary { Gen.oneOf(Cross, Naught) }
implicit def arbitraryXPosition: Arbitrary[Int] = Arbitrary { Gen.choose(0, 6) }
implicit def arbitraryBoardMove: Arbitrary[(Int, Coin)] = Arbitrary {
for {
coin <- arbitraryCoin.arbitrary
x <- arbitraryXPosition.arbitrary
} yield (x, coin)
}
implicit def arbitraryBoard: Arbitrary[Board] = Arbitrary {
for {
moves <- Gen.listOf1(arbitraryBoardMove.arbitrary)
} yield {
val board = new Board
moves.foreach { case (x, coin) =>
try { board.move(x, coin) } catch { case e => () }}
board
}
}
}
object Cross extends Coin {
override def toString = "x"
}
object Naught extends Coin {
override def toString = "o"
}
sealed trait Coin
The e1 property I've implemented is not the real thing because it doesn't really check that we moved the coin to the nearest empty slot, which is what your code and your API suggests. You will also want to change the generated data so that the Boards are generated with an alternation of x and o. That should be a great way to learn how to use ScalaCheck!
I suggest you throw all that code out -- well, save it somewhere, but start from zero using TDD.
The Specs2 site has plenty examples of how to write tests, but use TDD -- test driven design -- to do it. Adding tests after the fact is suboptimal, to say the least.
So, think of the most simple case you want to handle of the most simple feature, write a test for that, see it fail, write the code to fix it. Refactor if necessary, and repeat for the next most simple case.
If you want help with how to do TDD in general, I heartily endorse the videos about TDD available on Clean Coders. At the very least, watch the second part where Bob Martin writes a whole class TDD-style, from design to end.
If you know how to do testing in general but are confused about Scala or Specs, please be much more specific about what your questions are.