runtime using measureTimeMillis - kotlin

I'm attempting to compare different run-times for simple blocks of code, but continue to get 0 returned. What can I do to get a better approximation for the execution time?
private var trackConstantTime: Long? = null
this.trackConstantTime = measureTimeMillis {
/* determine if a given number is even or odd */
var n = (0..(Int.MAX_VALUE)).random()
if(n % 2 == 0) "Even" else "Odd"
}
println("O(1), Constant Time for fxConstantTime(...):${TimeUnit.MILLISECONDS.toSeconds(trackConstantTime!!)}")
Similarly if I'll attach another example that's returning 0 for the runtime.
private var trackLinearTime: Long? = null
private var uL: MutableList<Int> = mutableListOf()
for(i in 0..100){
this.uL.add( ((0)..(100)).random() )
}
this.trackLinearTime = measureTimeMillis {
/* determine the maximum value in an unsorted array */
var max: Int = 0
for(i in 0 until uL.size) {
if (uL[i] > max) max = uL[i]
println(max)
}
}
println("O(n), Linear Time for fxLinearTime(...):${TimeUnit.MILLISECONDS.toSeconds(trackLinearTime!!)}")


Maybe try to measure time in nanoseconds:
this.trackLinearTime = measureNanoTime {
...
}

Related

Can someone explain why the below Kotlin code produces incorrect expected result?

Can someone explain why the below code produces [2,3,5,6,7,8,9,10,11,12]?
I know it has something to do with filter function is deferred to the last element but I don't see the picture. It would even be better if you can visualise it. Thank you so much.
val primes: Sequence<Int> = sequence {
var numbers = generateSequence(2) { it + 1 }
var prime: Int
while (true) {
prime = numbers.first()
yield(prime)
numbers = numbers.drop(1).filter { it % prime != 0 }
}
}
print(primes.take(10).toList())

it's because you change prime variable in filter closure. For example, on the second step you have numbers as .filter { it % prime != 0 }.filter { it % prime != 0 } but the prime is one variable, and it is equal to 3
Correct version:
val primes: Sequence<Int> = sequence {
var numbers = generateSequence(2) { it + 1 }
while (true) {
val prime = numbers.first()
yield(prime)
numbers = numbers.drop(1).filter { it % prime != 0 }
}
}
print(primes.take(10).toList())

Read a sequence of numbers of undefined size & print the largest number & position of its first occurrence

I need to read a sequence of numbers of undefined size & prints the largest number & the position of its first occurrence
Can anyone help with this code:
import java.util.Scanner
fun main() {
val scan = Scanner(System.`in`)
val num = scan.nextInt()
var max = Int.MIN_VALUE
var pos = 0
var i = 1
do {
if (max < num) {
max = num
pos = i
}
i++
} while (scan.hasNext())
print("$max $pos")
}

You just need to read a new number in each iteration:
import java.util.Scanner
fun main() {
val scan = Scanner(System.`in`)
var max = Int.MIN_VALUE
var pos = 0
var i = 1
while (scan.hasNext()) {
// Read a new number here
val num = scan.nextInt()
if (max < num) {
max = num
pos = i
}
i++
}
print("$max $pos")
}

My solution to this task
This is a simple task, it can be solved in a simple way without using a “java.util.Scanner”. You just need to read a new number in each iteration.
fun main() {
var pos = 0
var max = 0
var count = 1
while (true) {
val input = readlnOrNull()
if (input == null) break
val num = input.toInt()
if (pos == 0 || num > max) {
max = num
pos = count
}
count++
}
print("$max $pos")
}

how to increase the size limit of a mutable list in kotlin?

I was attempting to solve the multiset question (https://codeforces.com/contest/1354/problem/D) on codeforces using Fenwick Tree Data structure. I passed the sample test cases but got the memory limit error after submitting, the testcase is mentioned below.
(Basically the testcase is:
1000000 1000000
1.............1 //10^6 times
-1...........-1 //10^6 times).
I tried similar testcase in my IDE and got the below mentioned error.
(Similar to above, the testcase I provided is:
1000000 1
1.............1 //10^6 times
-1
)
Exception in thread "main" java.lang.IndexOutOfBoundsException: Index 524289 out of bounds for length 524289
at java.base/jdk.internal.util.Preconditions.outOfBounds(Preconditions.java:64)
at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Preconditions.java:70)
at java.base/jdk.internal.util.Preconditions.checkIndex(Preconditions.java:248)
at java.base/java.util.Objects.checkIndex(Objects.java:373)
at java.base/java.util.ArrayList.get(ArrayList.java:426)
at MultisetKt.main(multiset.kt:47)
at MultisetKt.main(multiset.kt)
Here is my code:
private fun readInt() = readLine()!!.split(" ").map { it.toInt() }
fun main() {
var (n, q) = readInt()
var list = readInt() //modify the list to store it from index 1
var finalList = listOf(0) + list
val query = readInt()
var bit = MutableList(n+1){0}
fun update(i:Int, value:Int) {
var index = i
while(index < n){
bit.set (index , bit[index] + value)
index += (index and -index)
}
}
fun rangefunc(i:Int): Int {
var su = 0
var index = i
while(index > 0){
su += bit[index]
index -= (index and -index)
}
return su
}
fun find(x:Int):Int {
var l = 1
var r = n
var ans = n
var mid = 0
while (l <= r) {
mid = (l + r) / 2
if (rangefunc(mid) >= x) {
ans = mid
r = mid - 1
} else {
l = mid + 1
}
}
return ans
}
for (i in 1..n) {
update(finalList[i], 1)
}
for (j in 0..q - 1) {
if (query[j] > 0) {
update(query[j], 1)
} else {
update(find(-query[j]), -1)
}
}
if(rangefunc(n) == 0){
println(0)
}else{
println(find(1))
}
}
I believe this is because the BITlist is not able to store 10^6 elements but not sure. Please let me know what changes should I make in my code also any additional advice on how to deal with such cases in the future.
Thank you in advance :)

An ArrayList can store over 2 billion items (2 * 10^9). That is not your issue. ArrayIndexOutOfBoundsException is for trying to access an index of an ArrayList that is less than zero or greater than or equal to its size. In other words, an index that it doesn't yet contain.
There's more code there than I have time to debug. But I would start at the line that the stack trace points to and see how it's possible for you to attempt to call bit[index] with an index that equals the size of the ArrayList.
To answer your literal question, you can use LinkedList explicitly as your type of MutableList to avoid the size restriction, but it is heavier and it is slower when accessing elements by index.

Kotlin - The caracter literal does not conform expect type Int

I'm struggling with types with my program, I've been asked to do it in JS first and it worked fine but now I can't achieve the result.
Do you think I should make another 'algorithm' ? In advance, thank you for your time.
fun main(){
// the idea is to put numbers in a box
// that cant be larger than 10
val data = "12493419133"
var result = data[0]
var currentBox = Character.getNumericValue(data[0])
var i = 1
while(i < data.length){
val currentArticle = Character.getNumericValue(data[i])
currentBox += currentArticle
println(currentBox)
if(currentBox <= 10){
result += Character.getNumericValue(currentArticle)
}else{
result += '/'
//var resultChar = result.toChar()
// result += '/'
currentBox = Character.getNumericValue(currentArticle)
result += currentArticle
}
i++
}
print(result) //should print 124/9/341/91/33
}

The result is actually of a Char type, and the overload operator function + only accepts Int to increment ASCII value to get new Char.
public operator fun plus(other: Int): Char
In idomatic Kotlin way, you can solve your problem:
fun main() {
val data = "12493419133"
var counter = 0
val result = data.asSequence()
.map(Character::getNumericValue)
.map { c ->
counter += c
if (counter <= 10) c.toString() else "/$c".also{ counter = c }
}
.joinToString("") // terminal operation, will trigger the map functions
println(result)
}
Edit: If the data is too large, you may want to use StringBuilder because it doesn't create string every single time the character is iterated, and instead of using a counter of yourself you can use list.fold()
fun main() {
val data = "12493419133"
val sb = StringBuilder()
data.fold(0) { acc, c ->
val num = Character.getNumericValue(c)
val count = num + acc
val ret = if (count > 10) num.also { sb.append('/') } else count
ret.also { sb.append(c) } // `ret` returned to ^fold, next time will be passed as acc
}
println(sb.toString())
}

If you want a result in List<Char> type:
val data = "12493419133"
val result = mutableListOf<Char>()
var sum = 0
data.asSequence().forEach {
val v = Character.getNumericValue(it)
sum += v
if (sum > 10) {
result.add('/')
sum = v
}
result.add(it)
}
println(result.joinToString(""))

Kotlin decomposing numbers into powers of 2

Hi I am writing an app in kotlin and need to decompose a number into powers of 2.
I have already done this in c#, PHP and swift but kotlin works differently somehow.
having researched this I believe it is something to do with the numbers in my code going negative somewhere and that the solution lies in declaring one or more of the variable as "Long" to prevent this from happening but i have not been able to figure out how to do this.
here is my code:
var salads = StringBuilder()
var value = 127
var j=0
while (j < 256) {
var mask = 1 shl j
if(value != 0 && mask != 0) {
salads.append(mask)
salads.append(",")
}
j += 1
}
// salads = (salads.dropLast()) // removes the final ","
println("Salads = $salads")
This shoud output the following:
1,2,4,8,16,32,64
What I actually get is:
1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,131072,262144,524288,1048576,2097152,4194304,8388608,16777216,33554432,67108864,134217728,268435456,536870912,1073741824,-2147483648,1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,131072,262144,524288,1048576,2097152,4194304,8388608,16777216,33554432,67108864,134217728,268435456,536870912,1073741824,-2147483648,1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,131072,262144,524288,1048576,2097152,4194304,8388608,16777216,33554432,67108864,134217728,268435456,536870912,1073741824,-2147483648,1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,131072,262144,524288,1048576,2097152,4194304,8388608,16777216,33554432,67108864,134217728,268435456,536870912,1073741824,-2147483648,1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,131072,262144,524288,1048576,2097152,4194304,8388608,16777216,33554432,67108864,134217728,268435456,536870912,1073741824,-2147483648,1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,131072,262144,524288,1048576,2097152,4194304,8388608,16777216,33554432,67108864,134217728,268435456,536870912,1073741824,-2147483648,1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,131072,262144,524288,1048576,2097152,4194304,8388608,16777216,33554432,67108864,134217728,268435456,536870912,1073741824,-2147483648,1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,131072,262144,524288,1048576,2097152,4194304,8388608,16777216,33554432,67108864,134217728,268435456,536870912,1073741824,-2147483648,
Any ideas?

This works for the one input that you specified, at the very least:
fun powersOfTwo(value :Long): String {
val result = ArrayList<String>()
var i = 0
var lastMask = 0
while (lastMask < value) {
val mask = 1 shl i
if (value != 0.toLong() && mask < value) {
result.add(mask.toString())
}
lastMask = mask
i += 1
}
return result.joinToString(",")
}
Ran it in a unit test:
#Test
fun addition_isCorrect() {
val result = powersOfTwo(127)
assertEquals("1,2,4,8,16,32,64", result)
}
Test passed.

You can get a list of all powers of two that fit in Int and test each of them for whether the value contains it with the infix function and:
val value = 126
val powersOfTwo = (0 until Int.SIZE_BITS).map { n -> 1 shl n }
println(powersOfTwo.filter { p -> value and p != 0}.joinToString(","))
// prints: 2,4,8,16,32,64
See the entire code in Kotlin playground: https://pl.kotl.in/f4CZtmCyI

Hi I finally managed to get this working properly:
fun decomposeByTwo(value :Int): String {
val result = ArrayList<String>()
var value = value
var j = 0
while (j < 256) {
var mask = 1 shl j
if ((value and mask) != 0) {
value -= mask
result.add(mask.toString())
}
j += 1
}
return result.toString()
}
I hope this helps someone trying to get a handle on bitwise options!

Somehow you want to do the "bitwise AND" of "value" and "mask" to determine if the j-th bit of "value" is set. I think you just forgot that test in your kotlin implementation.