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What does itertools. combinations() do ? It returns r length subsequences of elements from the input iterable. Combinations are emitted in lexicographic sort order.
Python – Itertools Combinations() function combinations() provides us with all the possible tuples a sequence or set of numbers or letters used in the iterator and the elements are assumed to be unique on the basis of there positions which are distinct for all elements.
An algorithm has 'sqrt' (or √ ) time complexity when the number of operations increases dependant on the number of primes under the square root of the given number.
To calculate the combinations of a dictionary in Python, use the itertools. combinations() method. The combinations() method takes a dictionary as an argument and returns all the possible combinations of the dictionary elements. Let's define a dictionary and perform the combinations on the item of the tuple.
itertools.combinations in python is a powerful tool for finding all combination of r terms, however, I want to know about its computational complexity.
Let's say I want to know the complexity in terms of n and r, and certainly it will give me all the r terms combination from a list of n terms.
According to the Official document, this is the rough implementation.
def combinations(iterable, r):
# combinations('ABCD', 2) --> AB AC AD BC BD CD
# combinations(range(4), 3) --> 012 013 023 123
pool = tuple(iterable)
n = len(pool)
if r > n:
return
indices = list(range(r))
yield tuple(pool[i] for i in indices)
while True:
for i in reversed(range(r)):
if indices[i] != i + n - r:
break
else:
return
indices[i] += 1
for j in range(i+1, r):
indices[j] = indices[j-1] + 1
yield tuple(pool[i] for i in indices)
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