Build a pile of Cubes in Kotlin

The challenge

Your task is to construct a building which will be a pile of n cubes. The cube at the bottom will have a volume of n^3, the cube above will have volume of (n-1)^3 and so on until the top which will have a volume of 1^3.

You are given the total volume m of the building. Being given m can you find the number n of cubes you will have to build?

The parameter of the function findNb (find_nb, find-nb, findNb) will be an integer m and you have to return the integer n such as n^3 + (n-1)^3 + … + 1^3 = m if such a n exists or -1 if there is no such n.

Examples:

findNb(1071225) –> 45

findNb(91716553919377) –> -1

The solution in Kotlin code

Option 1:

package solution

object ASum {

    fun findNb(m: Long): Long {
        var n: Long = 0
        var cubeSize: Long = 0
        while (cubeSize < m) {
            cubeSize += n * n * n
            n++
        }
        return if (cubeSize == m) n - 1 else -1
    }
}

Option 2:

package solution

object ASum {

    fun findNb(m: Long): Long {
        var sum = 0L
        return generateSequence(1L) { it + 1 }
            .onEach { sum += it*it*it }
            .takeWhile { sum <= m }
            .lastOrNull { sum == m } 
            ?: -1
    }
}

Option 3:

package solution
import kotlin.math.pow

object ASum {
    fun findNb(m: Long): Long {
        var i = 0.0;
        var n = 0.0;
        while(n < m) {
            n += (i).pow(3);
            if(n.toLong() == m)
                return i.toLong();
            i++;
        }
        return -1;
    }
}

Test cases to validate our solution

package solution

import org.junit.Test
import kotlin.test.assertEquals

class  ASumTest {

    private fun testing(n: Long, expected: Long) {
        var actual = ASum.findNb(n)
        assertEquals(expected, actual)
    }
    @Test
    fun fixedTests() {
        testing(56396345062501, -1)
        testing(6132680780625, 2225)
        testing(28080884739601, -1)
        
    }
}
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