Kotlin's solution for Hackerrank's Lonely Integer excercise https://www.hackerrank.com/challenges/lonely-integer/problem

LonelyInteger.kt

package hakerrank

import java.io.*
import java.math.*
import java.security.*
import java.text.*
import java.util.*
import java.util.concurrent.*
import java.util.function.*
import java.util.regex.*
import java.util.stream.*
import kotlin.collections.*
import kotlin.comparisons.*
import kotlin.io.*
import kotlin.jvm.*
import kotlin.jvm.functions.*
import kotlin.jvm.internal.*
import kotlin.ranges.*
import kotlin.sequences.*
import kotlin.text.*

/**
 * 
 * https://www.hackerrank.com/challenges/lonely-integer/problem
 * 
 * You will be given an array of integers. All of the integers except one occur twice. That one is unique in the array.
 * Given an array of integers, find and print the unique element. For example, a = [1,2,3,4,3,2,1], the unique element is 4.
 * Function Description:
 * Complete the lonelyinteger function in the editor below. It should return the integer which occurs only once in the input array.
 * lonelyinteger has the following parameter(s):
 * a: an array of integers
 * Input Format
 * The first line contains a single integer, n, denoting the number of integers in the array.
 * The second line contains n space-separated integers describing the values in a.
 * Constraints
 * 1<=n<100
 * It is guaranteed that n is an odd number and that there is one unique element.
 * 0<=a[i]<=100, where 0<=i<n.
 * Output Format
 * Print the unique integer in the array.
 */
// Complete the lonelyinteger function below.
fun lonelyinteger(a: Array<Int>): Int {
    val map = mutableMapOf<Int, Int>()
    a.forEach {
        if (!map.containsKey(it)) {
            map[it] = it
        }else{
            map.remove(it)
        }
    }
    var lonely = 0
    for (entry in map) lonely = entry.value
    return lonely
}

fun main(args: Array<String>) {
    val scan = Scanner(System.`in`)

    val n = scan.nextLine().trim().toInt()

    val a = scan.nextLine().split(" ").map{ it.trim().toInt() }.toTypedArray()

    val result = lonelyinteger(a)

    println(result)
}