How should I fix my code for Sock Merchant with runtime error

Question

Though I wrote a code for Sock Merchant on HackerRank, I've stacked on one error.

I tried to visualize the transition of the array named ar, but I have not found the reason why the error list index out of range is caused yet.

Code:

#!/bin/python3

import math
import os
import random
import re
import sys

# Complete the sockMerchant function below.
def sockMerchant(n, ar):
    num = 0
    for i in range(len(ar)):
        if ar.count(ar[i]) > 1:
            if ar.count(ar[i]) % 2 == 0:
                num += ar.count(ar[i]) // 2
                print(num) #2
                print(ar[i])
                while ar[i] in ar:
                    ar.remove(ar[i])
                #[20, 20, 30, 50, 20]
            else:
                num += math.ceil(ar.count(ar[i]) // 2)
                print(num) #3
                while ar[i] in ar:
                    ar.remove(ar[i])
                #[30, 50]
        else:
            continue

    return num #3

if __name__ == '__main__':
    n = 9
    ar =[10, 20, 20, 10, 10, 30, 50, 10, 20]

    result = sockMerchant(n, ar)
    print(result)

Output:

Finished in N/A
2
10
IndexError: list index out of range
Line 18 in sockMerchant (Solution.py)
Line 36 in <module> (Solution.py)

Answer 1

static int sockMerchant(int n, int ar[]) {
    int num_pairs = 0;
    if (ar.length == 0) {
        return num_pairs;
    }
    Set < Integer > set = new HashSet();
    for (int i = 0; i < ar.length; i++) {
        if (!set.contains(ar[i])) {
            set.add(ar[i]);
        } else {
            num_pairs++;
            set.remove(ar[i]);
        }
    }
    return num_pairs;
}

Answer 2

Trying another approach in Python for the "Sock Merchant" challenge.

In here I used the Counter function by importing from the "collections" Library.

After arranging it into Dictionary values I counted the number of pairs which are more than one by truncating it... that is n//2.

from collections import Counter

#You can use this list #     
#or possibly any other ones.
my_lst = [50, 20, 30, 90, 30, 20, 50, 20, 90]

def sock_merchant(my_lst):

    a = dict(Counter(my_lst))
    print(a)

    pairs = []
    for value in a.values():
        if value > 1:
        pairs.append(value//2)
    return sum(pairs)

sock_merchant(my_lst)

Answer 3

def sockMerchant(n, ar):
s=0
for val in Counter(ar).values():
    s+=val//2
return s