more_non_unique_elements.js

function countDuplicates(numbers){
    //[1,1,1,2,3,3,4,5,6]
    //[1,3,1,4,5,1,6,3,2]
    numbers.sort((a,b) => a - b)
    // sort the array
    let count = 0
    let left = 0
    let right = 1
    //loop through numbers
    while (right < numbers.length){
        if(numbers[left] == numbers[right]){
            count++
            while(numbers[left] == numbers[right]){
                right++
            }
            left = right
            right++
        }else{
            left = right
            right++
        } 
    }
    return count
}
console.log(countDuplicates([1,3,1,4,5,1,6,3,2]))