I am trying to write a program that can find the roots of a quadratic equation using Scala. The input should be a quadratic equation in the form ax^2+bx+c (e.g: 5x^2+2x+3) as a string.
I managed to code the calculation of the roots but am having trouble extracting the coefficients from the input. Here's the code I wrote for extracting the coefficients so far:
def getCoef(poly: String) = {
var aT: String = ""
var bT: String = ""
var cT: String = ""
var x: Int = 2
for (i <- poly.length - 1 to 0) {
val t: String = poly(i).toString
if (x == 2) {
if (t forall Character.isDigit) aT = aT + t(i)
else if (t == "^") {i = i + 1; x = 1}
}
else if (x == 1) {
if (t forall Character.isDigit) bT = bT + t(i)
else if (t == "+" || t == "-") x = 0
}
else if (x == 0) {
if (t forall Character.isDigit) cT = cT + t(i)
}
val a: Int = aT.toInt
val b: Int = bT.toInt
val c: Int = cT.toInt
(a, b, c)
}
}
Simple solution with regex:
def getCoef(poly: String) = {
val polyPattern = """(\d+)x\^2\+(\d+)x\+(\d+)""".r
val matcher = polyPattern.findFirstMatchIn(poly).get
(matcher.group(1).toInt, matcher.group(2).toInt, matcher.group(3).toInt)
}
Does not handle all cases (e.g.: minus) and just throws an error if the input does not match the pattern, but it should get you going.
Related
I've been working on the scala recursion problem. I used to develop the program using loops and then use the concept of recursion to convert the existing loop problem in a recursive solution.
So I have written the following code to find the perfect number using loops.
def isPerfect(n: Int): Boolean = {
var sum = 1
// Find all divisors and add them
var i = 2
while ( {
i * i <= n
}) {
if (n % i == 0) if (i * i != n) sum = sum + i + n / i
else sum = sum + i
i += 1
}
// If sum of divisors is equal to
// n, then n is a perfect number
if (sum == n && n != 1) return true
false
}
Here is my attempt to convert it into a recursive solution. But I'm getting the incorrect result.
def isPerfect(n: Int): Boolean = {
var sum = 1
// Find all divisors and add them
var i = 2
def loop(i:Int, n:Int): Any ={
if(n%i == 0) if (i * i != n) return sum + i + n / i
else
return loop(i+1, sum+i)
}
val sum_ = loop(2, n)
// If sum of divisors is equal to
// n, then n is a perfect number
if (sum_ == n && n != 1) return true
false
}
Thank you in advance.
Here is a tail-recursive solution
def isPerfectNumber(n: Int): Boolean = {
#tailrec def loop(d: Int, acc: List[Int]): List[Int] = {
if (d == 1) 1 :: acc
else if (n % d == 0) loop(d - 1, d :: acc)
else loop(d - 1, acc)
}
loop(n-1, Nil).sum == n
}
As a side-note, functions that have side-effects such as state mutation scoped locally are still considered pure functions as long as the mutation is not visible externally, hence having while loops in such functions might be acceptable.
I want to generate a list of Tuple2 objects. Each tuple (a,b) in the list should meeting the conditions:a and b both are perfect squares,(b/30)<a<b
and a>N and b>N ( N can even be a BigInt)
I am trying to write a scala function to generate the List of Tuples meeting the above requirements?
This is my attempt..it works fine for Ints and Longs..But for BigInt there is sqrt problem I am facing..Here is my approach in coding as below:
scala> def genTups(N:Long) ={
| val x = for(s<- 1L to Math.sqrt(N).toLong) yield s*s;
| val y = x.combinations(2).map{ case Vector(a,b) => (a,b)}.toList
| y.filter(t=> (t._1*30/t._2)>=1)
| }
genTups: (N: Long)List[(Long, Long)]
scala> genTups(30)
res32: List[(Long, Long)] = List((1,4), (1,9), (1,16), (1,25), (4,9), (4,16), (4,25), (9,16), (9,25), (16,25))
Improved this using BigInt square-root algorithm as below:
def genTups(N1:BigInt,N2:BigInt) ={
def sqt(n:BigInt):BigInt = {
var a = BigInt(1)
var b = (n>>5)+BigInt(8)
while((b-a) >= 0) {
var mid:BigInt = (a+b)>>1
if(mid*mid-n> 0) b = mid-1
else a = mid+1
}; a-1 }
val x = for(s<- sqt(N1) to sqt(N2)) yield s*s;
val y = x.combinations(2).map{ case Vector(a,b) => (a,b)}.toList
y.filter(t=> (t._1*30/t._2)>=1)
}
I appreciate any help to improve in my algorithm .
You can avoid sqrt in you algorithm by changing the way you calculate x to this:
val x = (BigInt(1) to N).map(x => x*x).takeWhile(_ <= N)
The final function is then:
def genTups(N: BigInt) = {
val x = (BigInt(1) to N).map(x => x*x).takeWhile(_ <= N)
val y = x.combinations(2).map { case Vector(a, b) if (a < b) => (a, b) }.toList
y.filter(t => (t._1 * 30 / t._2) >= 1)
}
You can also re-write this as a single chain of operations like this:
def genTups(N: BigInt) =
(BigInt(1) to N)
.map(x => x * x)
.takeWhile(_ <= N)
.combinations(2)
.map { case Vector(a, b) if a < b => (a, b) }
.filter(t => (t._1 * 30 / t._2) >= 1)
.toList
In a quest for performance, I came up with this recursive version that appears to be significantly faster
def genTups(N1: BigInt, N2: BigInt) = {
def sqt(n: BigInt): BigInt = {
var a = BigInt(1)
var b = (n >> 5) + BigInt(8)
while ((b - a) >= 0) {
var mid: BigInt = (a + b) >> 1
if (mid * mid - n > 0) {
b = mid - 1
} else {
a = mid + 1
}
}
a - 1
}
#tailrec
def loop(a: BigInt, rem: List[BigInt], res: List[(BigInt, BigInt)]): List[(BigInt, BigInt)] =
rem match {
case Nil => res
case head :: tail =>
val a30 = a * 30
val thisRes = rem.takeWhile(_ <= a30).map(b => (a, b))
loop(head, tail, thisRes.reverse ::: res)
}
val squares = (sqt(N1) to sqt(N2)).map(s => s * s).toList
loop(squares.head, squares.tail, Nil).reverse
}
Each recursion of the loop adds all the matching pairs for a given value of a. The result is built in reverse because adding to the front of a long list is much faster than adding to the tail.
Firstly create a function to check if number if perfect square or not.
def squareRootOfPerfectSquare(a: Int): Option[Int] = {
val sqrt = math.sqrt(a)
if (sqrt % 1 == 0)
Some(sqrt.toInt)
else
None
}
Then, create another func that will calculate this list of tuples according to the conditions mentioned above.
def generateTuples(n1:Int,n2:Int)={
for{
b <- 1 to n2;
a <- 1 to n1 if(b>a && squareRootOfPerfectSquare(b).isDefined && squareRootOfPerfectSquare(a).isDefined)
} yield ( (a,b) )
}
Then on calling the function with parameters generateTuples(5,10)
you will get an output as
res0: scala.collection.immutable.IndexedSeq[(Int, Int)] = Vector((1,4), (1,9), (4,9))
Hope that helps !!!
I have an array of numbers separated by comma as shown:
a:{108,109,110,112,114,115,116,118}
I need the output something like this:
a:{108-110, 112, 114-116, 118}
I am trying to group the continuous numbers with "-" in between.
For example, 108,109,110 are continuous numbers, so I get 108-110. 112 is separate entry; 114,115,116 again represents a sequence, so I get 114-116. 118 is separate and treated as such.
I am doing this in Spark. I wrote the following code:
import scala.collection.mutable.ArrayBuffer
def Sample(x:String):ArrayBuffer[String]={
val x1 = x.split(",")
var a:Int = 0
var present=""
var next:Int = 0
var yrTemp = ""
var yrAr= ArrayBuffer[String]()
var che:Int = 0
var storeV = ""
var p:Int = 0
var q:Int = 0
var count:Int = 1
while(a < x1.length)
{
yrTemp = x1(a)
if(x1.length == 1)
{
yrAr+=x1(a)
}
else
if(a < x1.length - 1)
{
present = x1(a)
if(che == 0)
{
storeV = present
}
p = x1(a).toInt
q = x1(a+1).toInt
if(p == q)
{
yrTemp = yrTemp
che = 1
}
else
if(p != q)
{
yrTemp = storeV + "-" + present
che = 0
yrAr+=yrTemp
}
}
else
if(a == x1.length-1)
{
present = x1(a)
yrTemp = present
che = 0
yrAr+=yrTemp
}
a = a+1
}
yrAr
}
val SampleUDF = udf(Sample(_:String))
I am getting the output as follows:
a:{108-108, 109-109, 110-110, 112, 114-114, 115-115, 116-116, 118}
I am not able to figure out where I am going wrong. Can you please help me in correcting this. TIA.
Here's another way:
def rangeToString(a: Int, b: Int) = if (a == b) s"$a" else s"$a-$b"
def reduce(xs: Seq[Int], min: Int, max: Int, ranges: Seq[String]): Seq[String] = xs match {
case y +: ys if (y - max <= 1) => reduce(ys, min, y, ranges)
case y +: ys => reduce(ys, y, y, ranges :+ rangeToString(min, max))
case Seq() => ranges :+ rangeToString(min, max)
}
def output(xs: Array[Int]) = reduce(xs, xs.head, xs.head, Vector())//.toArray
Which you can test:
println(output(Array(108,109,110,112,114,115,116,118)))
// Vector(108-110, 112, 114-116, 118)
Basically this is a tail recursive function - i.e. you take your "variables" as the input, then it calls itself with updated "variables" on each loop. So here xs is your array, min and max are integers used to keep track of the lowest and highest numbers so far, and ranges is the output sequence of Strings that gets added to when required.
The first pattern (y being the first element, and ys being the rest of the sequence - because that's how the +: extractor works) is matched if there's at least one element (ys can be an empty list) and it follows on from the previous maximum.
The second is if it doesn't follow on, and needs to reset the minimum and add the completed range to the output.
The third case is where we've got to the end of the input and just output the result, rather than calling the loop again.
Internet karma points to anyone who can work out how to eliminate the duplication of ranges :+ rangeToString(min, max)!
here is a solution :
def combineConsecutive(s: String): Seq[String] = {
val ints: List[Int] = s.split(',').map(_.toInt).toList.reverse
ints
.drop(1)
.foldLeft(List(List(ints.head)))((acc, e) => if ((acc.head.head - e) <= 1)
(e :: acc.head) :: acc.tail
else
List(e) :: acc)
.map(group => if (group.size > 1) group.min + "-" + group.max else group.head.toString)
}
val in = "108,109,110,112,114,115,116,118"
val result = combineConsecutive(in)
println(result) // List(108-110, 112, 114-116, 118)
}
This solution partly uses code from this question: Grouping list items by comparing them with their neighbors
I try to implement a version of the Monte Carlo algorithm in Scala but i have a little problem.
In my first loop, i have a mismatch with Unit and Int, but I didn't know how to slove this.
Thank for your help !
import scala.math._
import scala.util.Random
import scala.collection.mutable.ListBuffer
object Main extends App{
def MonteCarlo(list: ListBuffer[Int]): List[Int] = {
for (i <- list) {
var c = 0.00
val X = new Random
val Y = new Random
for (j <- 0 until i) {
val x = X.nextDouble // in [0,1]
val y = Y.nextDouble // in [0,1]
if (x * x + y * y < 1) {
c = c + 1
}
}
c = c * 4
var p = c / i
var error = abs(Pi-p)
print("Approximative value of pi : $p \tError: $error")
}
}
var liste = ListBuffer (200, 2000, 4000)
MonteCarlo(liste)
}
A guy working usually with Python.
for loop does not return anything, so that's why your method returns Unit but expects List[Int] as return type is List[Int].
Second, you have not used scala interpolation correctly. It won't print the value of error. You forgot to use 's' before the string.
Third thing, if want to return list, you first need a list where you will accumulate all values of every iteration.
So i am assuming that you are trying to return error for all iterations. So i have created an errorList, which will store all values of error. If you want to return something else you can modify your code accordingly.
def MonteCarlo(list: ListBuffer[Int]) = {
val errorList = new ListBuffer[Double]()
for (i <- list) {
var c = 0.00
val X = new Random
val Y = new Random
for (j <- 0 until i) {
val x = X.nextDouble // in [0,1]
val y = Y.nextDouble // in [0,1]
if (x * x + y * y < 1) {
c = c + 1
}
}
c = c * 4
var p = c / i
var error = abs(Pi-p)
errorList += error
println(s"Approximative value of pi : $p \tError: $error")
}
errorList
}
scala> MonteCarlo(liste)
Approximative value of pi : 3.26 Error: 0.11840734641020667
Approximative value of pi : 3.12 Error: 0.02159265358979301
Approximative value of pi : 3.142 Error: 4.073464102067881E-4
res9: scala.collection.mutable.ListBuffer[Double] = ListBuffer(0.11840734641020667, 0.02159265358979301, 4.073464102067881E-4)
In Scala language, I want to write a function that yields odd numbers within a given range. The function prints some log when iterating even numbers. The first version of the function is:
def getOdds(N: Int): Traversable[Int] = {
val list = new mutable.MutableList[Int]
for (n <- 0 until N) {
if (n % 2 == 1) {
list += n
} else {
println("skip even number " + n)
}
}
return list
}
If I omit printing logs, the implementation become very simple:
def getOddsWithoutPrint(N: Int) =
for (n <- 0 until N if (n % 2 == 1)) yield n
However, I don't want to miss the logging part. How do I rewrite the first version more compactly? It would be great if it can be rewritten similar to this:
def IWantToDoSomethingSimilar(N: Int) =
for (n <- 0 until N) if (n % 2 == 1) yield n else println("skip even number " + n)
def IWantToDoSomethingSimilar(N: Int) =
for {
n <- 0 until N
if n % 2 != 0 || { println("skip even number " + n); false }
} yield n
Using filter instead of a for expression would be slightly simpler though.
I you want to keep the sequentiality of your traitement (processing odds and evens in order, not separately), you can use something like that (edited) :
def IWantToDoSomethingSimilar(N: Int) =
(for (n <- (0 until N)) yield {
if (n % 2 == 1) {
Option(n)
} else {
println("skip even number " + n)
None
}
// Flatten transforms the Seq[Option[Int]] into Seq[Int]
}).flatten
EDIT, following the same concept, a shorter solution :
def IWantToDoSomethingSimilar(N: Int) =
(0 until N) map {
case n if n % 2 == 0 => println("skip even number "+ n)
case n => n
} collect {case i:Int => i}
If you will to dig into a functional approach, something like the following is a good point to start.
First some common definitions:
// use scalaz 7
import scalaz._, Scalaz._
// transforms a function returning either E or B into a
// function returning an optional B and optionally writing a log of type E
def logged[A, E, B, F[_]](f: A => E \/ B)(
implicit FM: Monoid[F[E]], FP: Pointed[F]): (A => Writer[F[E], Option[B]]) =
(a: A) => f(a).fold(
e => Writer(FP.point(e), None),
b => Writer(FM.zero, Some(b)))
// helper for fixing the log storage format to List
def listLogged[A, E, B](f: A => E \/ B) = logged[A, E, B, List](f)
// shorthand for a String logger with List storage
type W[+A] = Writer[List[String], A]
Now all you have to do is write your filtering function:
def keepOdd(n: Int): String \/ Int =
if (n % 2 == 1) \/.right(n) else \/.left(n + " was even")
You can try it instantly:
scala> List(5, 6) map(keepOdd)
res0: List[scalaz.\/[String,Int]] = List(\/-(5), -\/(6 was even))
Then you can use the traverse function to apply your function to a list of inputs, and collect both the logs written and the results:
scala> val x = List(5, 6).traverse[W, Option[Int]](listLogged(keepOdd))
x: W[List[Option[Int]]] = scalaz.WriterTFunctions$$anon$26#503d0400
// unwrap the results
scala> x.run
res11: (List[String], List[Option[Int]]) = (List(6 was even),List(Some(5), None))
// we may even drop the None-s from the output
scala> val (logs, results) = x.map(_.flatten).run
logs: List[String] = List(6 was even)
results: List[Int] = List(5)
I don't think this can be done easily with a for comprehension. But you could use partition.
def getOffs(N:Int) = {
val (evens, odds) = 0 until N partition { x => x % 2 == 0 }
evens foreach { x => println("skipping " + x) }
odds
}
EDIT: To avoid printing the log messages after the partitioning is done, you can change the first line of the method like this:
val (evens, odds) = (0 until N).view.partition { x => x % 2 == 0 }