CODEWITHSUNDEEP
python
user587646
user587646

Reputation: 127

Find pairs of numbers in a list that add up to 10

Given a list of numbers, I would like to find all pairs of numbers that add up to 10.

How can I write a function to do this in Python?

Upvotes: 0

Views: 2085

Answers (3)

bolt
bolt

Reputation: 13

This question is pretty old, but I thought I would contribute my own answer because both of the provided solutions at time of writing have subtle errors: one only provides one pair of numbers that adds up to 10; the other re-uses numbers (ex., even though 5 is only in the list once, (5, 5) gets listed as a solution in addition to repeating the pairs).

Using the itertools library, you can do the following:

from itertools import combinations

def pair_sums(arr, expected=10):
     return [x for x in combinations(arr, 2) if sum(x) == expected]

arr1 = [2, 4, 5, 6, 8]
pair_sums(arr1)  # returns [(2, 8), (4, 6)]

arr2 = [2, 5, 7, 5, 9, 3]
pair_sums(arr2)  # returns [(5, 5), (7, 3)]

Upvotes: 0

Petar Ivanov
Petar Ivanov

Reputation: 93090

Just store the difference from 10 in a set:

def find(arr, total):
    d = set()
    for e in arr:
        if e in d:
            print total-e, e
            break
        d.add(total-e)

s = [1,5,3,10,11,7,2]
find(s, 10)

Upvotes: 5

Jayesh
Jayesh

Reputation: 235

l = [1, 3, 4, 5, 6, 7, 8, 9]
[(x,y) for x in l for y in l if x+y==10]

Upvotes: 3

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