Chefina and Swaps using Python

general
#1

It works for all test cases. But submission verdict is WA.
Can anyone help finding the mistake?
`from collections import Counter

for _ in range(int(input())):
n=int(input())
a=list(map(int,input().split()))
b=list(map(int,input().split()))
ac=Counter(a)
bc=Counter(b)
weird=(ac-bc)+(bc-ac)
temp=list(weird.values())
sumi=0
i=0
try:
while(i<len(temp)):
if(temp[i]%2==0):
sumi+=temp[i]
else:
raise Exception
i+=1
except Exception as e:
sumi=-1
if(sumi/4==sumi//4):
print(sumi//4)
else:
print(-1)`

Link to original solution: https://www.codechef.com/viewsolution/35520862

#2

You are just swapping the minimum unbalanced element with the maximum unbalanced element in both the arrays so that you can take min value as the cost for balancing 2 operations.
There is an operation which can cost lesser.
Through another path. That is the minimum element. For example A is 0 1 1 B is 0 2 2
Min operation will be with swapping with 0. Ans is 0.
Swap 0 and 2 , then swap 0 and 1. Cost = 0

#3

Check this snippet for optimal path for swaps
m is the minimum element, for going through this path, m needs to be swapped twice, so that it returns to its original array.
while(count>0)
{
ll swap= itr->second;
ll val= itr->first;
if(swap>count)
swap=count;

       	itr++;

         
         if(swap*val <= m* swap*2)
         	sum+= swap*val;
         else
         	sum+= m*swap*2;

         count-= swap;
       }