Find Duplicate Number

FindDuplicate.kt

import java.util.*

// How do you find the duplicate number on a given integer array?

fun main() {
   
    val arr = arrayListOf(4, 5, 8, 3, 4, 11,5,8, 15, 3,4,4)
    
	println(arr.groupingBy { 
            it
        }.eachCount().filter{
	        it.value>1
    })
}

/*
OUTPUT:

{4=4, 5=2, 8=2, 3=2}

*/