var input = [1, 2, 5, 5, 3, 1, 3, 1];

    var duplicates = input.reduce(function(acc, el, i, arr) {

    if (arr.indexOf(el) !== i && acc.indexOf(el) < 0) acc.push(el); return acc;

    }, []);

    console.log(duplicates);

const myArray = ['a', 'b', 'c', 'c', 'b', 'd'];

const elementCounts = {};

myArray.forEach(element => {

  elementCounts[element] = (elementCounts[element] || 0) + 1;

});

console.log(elementCounts);

//output

/*{

  a: 1,

  b: 2,

  c: 2,

  d: 1

}*/

const numbers = [1, 2, 3, 2, 4, 5, 5, 6];

​

const set = new Set(numbers);

​

const duplicates = numbers.filter(item => {

    if (set.has(item)) {

        set.delete(item);

    } else {

        return item;

    }

});

​

console.log(duplicates);

// [ 2, 5 ]

function findDuplicates(arr) {

    const duplicates = new Set()

  return arr.filter(item => {

    if (duplicates.has(item)) {

        return true

    }

    duplicates.add(item)

    return false

  })

}

const order = ["apple", "banana", "orange", "banana", "apple", "banana"];

​

const result = order.reduce(function (prevVal, item) {

    if (!prevVal[item]) {

        // if an object doesn't have a key yet, it means it wasn't repeated before

        prevVal[item] = 1;

    } else {

        // increase the number of repetitions by 1

        prevVal[item] += 1;

    }

​

    // and return the changed object

    return prevVal;

}, {}); // The initial value is an empty object.

​

console.log(result); // { apple: 2, banana: 3, orange: 1 } 

  const numbers = [1, 2, 3, 2, 4, 5, 5, 6];

​

let isDuplicate = false;

​

// Outer for loop

for (let i = 0; i < numbers.length; i++) {

    // Inner for loop

    for (let j = 0; j < numbers.length; j++) {

        // Skip self comparison

        if (i !== j) {

            // Check for duplicate

            if (numbers[i] === numbers[j]) {

                isDuplicate = true;

                // Terminate inner loop

                break;

            }

        }

        // Terminate outer loop

        if (isDuplicate) {

            break;

        }

    }

}

​

if (!isDuplicate) {

    console.log(`Array doesn't contain duplicates.`);

} else {

    console.log(`Array contains duplicates.`);

}

// Output: Array contains duplicates.

public class Main {

public static void main(String[] args) {

  int[] arr1 = {1,2,3,3,4};

  for (int i = 0; i < arr1.length-1 ; i++) {

    for (int j = 0; j < arr1.length; j++) {

      if (arr1[i]==arr1[j] && (j != i)){

      System.out.println("array's duplicate number: " +

      arr1[j]);

        }

      }

    }

    }

}

​

def FirstOccurrence ( array, n ) :

    beg = 0

    end = len(array) - 1

​

    while (beg <= end) :

​

        mid = int (beg + (end-beg)/2)

​

        if (array[mid] == n) :

            if (mid-1 >= 0 and array[mid-1] == n) :

               end = mid-1

               continue

​

            return mid 

​

        elif (array[mid] < n) :

            beg = mid + 1 

        else :

            end = mid - 1 

​

    return -1  

​

def LastOccurrence (array, n) :

    beg = 0

    end = len(array)-1

​

    while (beg <= end) :

​

        mid = int(beg + (end-beg)/2)

​

        if (array[mid] == n) :

            if (mid+1 < len(array) and array[mid+1] == n) :

               beg = mid + 1 

               continue

            return mid 

​

        elif (array[mid] < n) :

            beg = mid + 1 

        else :

            end = mid - 1

​

    return -1; 

​

array = [ 1, 2, 3, 9, 9, 9, 9, 10, 10, 12, 13 ]

n = int (input("Enter the number : "))

​

first_index = FirstOccurrence (array, n)

last_index  = LastOccurrence (array, n)

​

if (first_index == -1 or last_index == - 1) :

    print("Element does not exist")

else :

    print("First occurrence of " + str(n) + " is at index : " + str(first_index))

    print("Last occurrence of " + str(n) + " is at index : " + str(last_index))

    print("Total count : "+ str(last_index - first_index + 1)) 

​