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  1. Prepare
  2. Python
  3. Itertools
  4. Iterables and Iterators
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Iterables and Iterators

  • vyoma_patel
     + 0 comments
    from itertools import combinations
N = int(input())
letters = input().split()
K = int(input())

#Creating list of letters with r=K
combos = list(combinations(letters, K)) 

#Incrementing value of count by 1 if 'a' found in c
count = sum(1 for c in combos if 'a' in c) 

#Calculating count by total no. of c(tuples) in combos and rounding up to 3 decimal places
print(f"{count/len(combos):.3f}")