CODEWITHSUNDEEP
python
user17156350
user17156350

Reputation:

Python: Delete lists with same elements but in different order

I'm trying to make a program that calculates quadruplets (a^3+b^3=c^3+d^3). With my current code i get 8 answers within the domain of [1, 15], but as you'll see by the output, the answers are all the same but the order is switched around. My question is: how can i filter out the duplicates and just get one answer? (Sorry if i caused you a heart attack with my messy code)

Code:

interval = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
solutions = []

for a in interval:
    for b in interval:
        for c in interval:
            for d in interval:
                if a != c and b !=d:
                    if a != d and b != c:
                        if a**3+b**3 == c**3+d**3:
                            temp = [a, b, c, d]
                            solutions.append(temp)
                            
print(solutions)

Output:

[[1, 12, 9, 10], [1, 12, 10, 9], [9, 10, 1, 12], [9, 10, 12, 1], [10, 9, 1, 12], [10, 9, 12, 1], [12, 1, 9, 10], [12, 1, 10, 9]]

Thanks in advance!

Upvotes: 1

Views: 197

Answers (4)

Jasmijn
Jasmijn

Reputation: 10452

Here is a solution that involves itertools.product and sets of sets of sets:

from itertools import product

interval = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
solutions = set()

for a, b, c, d in product(interval, repeat=4):
    if a != c and b != d and a != d and b != c:
        if a ** 3 + b ** 3 == c ** 3 + d ** 3:
            left_side = frozenset({a, b})
            right_side = frozenset({c, d})
            equality = frozenset({left_side, right_side})
            solutions.add(equality)

print(solutions)

This makes use of the fact that a and b can be swapped without affecting the equality, and the same goes for c and d, and (a, b) can be swapped with (c, d).

Upvotes: 0

Mojtaba Valizadeh
Mojtaba Valizadeh

Reputation: 766

You can also add an order to your solutions. For example, according to your function, you can add this line to your conditions:

if a < b and c < d and a < c:

Then you only have:

Output : [[1, 12, 9, 10]]

Upvotes: 0

Blckknght
Blckknght

Reputation: 104712

You can use itertools.combinations to produce ordered 4-tuples from your list with much less duplication. But it does present a new problem, that you don't actually want ordered values, since your equation can't possibly be satisfied with a < b < c < d, since you'd be adding up the cubes of the two smallest values which will always be smaller than the cubes of the two largest values.

That does lead us to a key insight. We never want to pair up the two largest and two smallest values from our four-tuple. Further, we don't even want to pair up the smaller of the first two values with the smaller of the second two values, because again, they cubes will always wind up smaller than the other pair. So we can just always pair up the largest value with the smallest value and pair up the two middle values. So if they're ordered (a < b < c < d), you want a**3 + d**3 and b**3 + c**3. Here's how I'd do that in code:

import itertools as it

interval = range(1, 16)

results = [[a, d, b, c] for a, b, c, d in it.combinations(interval, 4)
                        if a**3 + d**3 == b**3 + c**3]

Upvotes: 4

John Coleman
John Coleman

Reputation: 51998

As ShadowRanger mentioned in the comments, itertools.combinations is the tool to use:

from itertools import combinations
solutions = []
for (a,b),(c,d) in combinations(combinations(range(1,16),2),2):
    if a**3 + b**3 == c**3 + d**3:
        solutions.append((a,b,c,d))
print(solutions)

prints [(1, 12, 9, 10)]

Upvotes: 6

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