I am trying to solve an algorithm for finding max subarray in an array, using the max() function that compares 2 Ints and returns the bigger value.

I looked at other questions on stack overflow and no one refers to this problem so I must be doing something very basic wrong here. Also looked at the .math Library on Kotlin:

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.math/max.html#:~:text=Returns the greater of two,then the result is NaN .&text=Returns the greater of two values.,-Common

To try and understand but again, I put two Ints in a max() function and I keep getting type mismatch as it requires a Boolean.

I even went and created my own function (maxCustom()) in the code below to try and bypass that, stating specifically that it receives two Ints and returns an Int, and I still get the same Boolean type mismatch.

fun maximumSubarray(nums: List<Int>): Int {

    fun maxCustom(a: Int, b: Int): Int {
        return if (a > b) a
        else b
    }

    var maxGlobal = 0
    var maxCurrent = maxGlobal == nums[0]

    for (num in nums[1] .. nums[nums.size-1]) {
        maxCurrent = maxCustom(a = nums[num], b = maxCurrent   nums[num])

        if (maxCurrent > maxGlobal) {
            maxGlobal = maxCurrent
        }
    }


    return maxGlobal

}


fun main() {
    val nums = listOf(-2, 3, 2, -1)
    val solution = maximumSubarray(nums)
    println(solution)
}

Thanks for the help

CodePudding user response：

As @Sam points out, your maxCurrent variable is a Boolean, not an Integer. As such, when you try to assign an Integer to maxCurrent, it fails.

To avoid such errors in the future, you should instantiate your variables with types using syntax such as var maxCurrent: Int = maxGlobal.

N.B.: For this particular problem it would be better to instantiate your maxGlobal with a declaration such as var maxGlobal: Int = Int.MIN_VALUE. This is the minimum value an Int can have. You should do this as the maximum subarray could be less than 0!