Given three arrays of integers, return the sum of elements that are common in all three arrays.

For example: 

```
common([1,2,3],[5,3,2],[7,3,2]) = 5 because 2 & 3 are common in all 3 arrays
common([1,2,2,3],[5,3,2,2],[7,3,2,2]) = 7 because 2,2 & 3 are common in the 3 arrays
```

More examples in the test cases. 

Good luck!

Difficulty: introductory

Starter code:

def common(a,b,c):
	

Solutions:
from collections import Counter
def common(a,b,c):
    return sum((Counter(a) & Counter(b) & Counter(c)).elements())

from functools import reduce
from operator import and_
from collections import Counter

def common(a,b,c):
    return sum(reduce(and_,map(Counter, (a,b,c))).elements())

from collections import Counter
from functools import reduce
from operator import and_

def common(*args):
    return sum(key * value for key, value in reduce(and_, map(Counter, args)).items())

from collections import Counter

def common(a, b, c):
    abc = Counter(a) & Counter(b) & Counter(c)
    return sum(n * q for n, q in abc.items())

# Python is nice
from collections import Counter
from operator import mul, and_
from itertools import starmap
from functools import reduce

def common(*args):
    return sum(starmap(mul, reduce(and_, map(Counter, args)).items()))

def common(a,b,c): 
    a.sort() ; b.sort() ; c.sort()
    i = j = k = c1 = 0
    while i < len(a) and j < len(b) and k < len(c):
        if a[i] == b[j] == c[k]:
            c1 += a[i]
            i += 1 ; j += 1 ; k += 1
        elif a[i] < b[j] : i += 1
        elif b[j] < c[k] : j += 1
        else : k += 1
    return c1

def common(a,b,c):
    d = set(a)&set(b)&set(c)
    a = [i for i in a if i in d]
    b = [i for i in b if i in d]
    c = [i for i in c if i in d]
    return sum([i*min(a.count(i), b.count(i), c.count(i)) for i in d])

from collections import Counter

def common(a, b, c):
    abc = Counter(a) & Counter(b) & Counter(c)
    return sum(abc.elements())

common=lambda*a,c=__import__('collections').Counter:sum(__import__('functools').reduce(c.__and__,map(c,a)).elements())

from collections import Counter

def common(a,b,c):
    counts_a, counts_b, counts_c = Counter(a), Counter(b), Counter(c)
    sum = 0
    for n in (set(counts_a.keys()) & set(counts_b.keys())) & set(counts_c.keys()):
        sum += n * min([counts_a[n], counts_b[n], counts_c[n]])
    return sum