Compare Two Lists and Find Missing Element in Second List - Python

Compare Two Lists and Find Missing Element in Second List - Python

Solutions

Iterating smaller list and removing the element from other list #516 ns

def finder(a, b):
  for i in b:
    a.remove(i)
  return a

Sorting, Zipping, Comparing each pair and returning first occurrence of mismatching pair #984 ns

def finder2(a,b):
  a.sort()
  b.sort()
  for num1, num2, in zip(a,b):
    if num1!=num2:
      return num1
  return a[-1]

Adding to dictionary and counting occurrence #5250 ns

import collections
def finder3(a,b):
  
  d = collections.defaultdict(int)
  
  for n in b:
    d[n] += 1
  
  for m in a:
    if d[m] == 0:
      return m
    else:
      d[m] -= 1

Subtracting sum of smaller list from larger list #538 ns

def finder4(a,b):
  return sum(a) - sum(b)

Testing Time

a = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]
b = [19,10,20,9,11,6,12,3,13,2,14,4,15,8,16,5,17,1,18]
%timeit finder(a, b)
%timeit finder2(a, b)

%timeit finder3(a, b)

%timeit finder4(a, b)

Output

The slowest run took 12.04 times longer than the fastest. This could mean that an intermediate result is being cached. 1000000 loops, best of 3: 516 ns per loop The slowest run took 26.17 times longer than the fastest. This could mean that an intermediate result is being cached. 1000000 loops, best of 3: 984 ns per loop 100000 loops, best of 3: 5.25 µs per loop The slowest run took 5.56 times longer than the fastest. This could mean that an intermediate result is being cached. 1000000 loops, best of 3: 538 ns per loop