Python - Construct Sum pairs equal to K

Python – Construct Sum pairs equal to K

Last Updated : 08 Jun, 2020

Sometimes, while working with Python lists, we can have problem in which we need to extract pairs which have sum equal to K. This kind of problem is common and can have application in domains such as web development and day-day programming. Let’s discuss certain ways in which this task can be performed.

Input : 
test_list = [1, 9, 5, 5, 7]
K = 10
Output : [(1, 9), (5, 5)]


Input : 
test_list = [1, 9, 7, 8, 3]
K = 12
Output : [(9, 3)]

Method #1 : Using list comprehension + sum()
The combination of above functions can be used to solve this problem. In this, we perform the task of finding summation equal to K using sum() and list comprehension is used to logic and pair building.

# Python3 code to demonstrate working of  
# Construct Sum pairs equal to K 
# Using list comprehension + sum() 
  
# initializing list 
test_list = [3, 4, 0, 5, 2] 
  
# printing original list 
print("The original list is : " + str(test_list)) 
  
# initializing K 
K = 7
  
# Construct Sum pairs equal to K 
# Using list comprehension + sum() 
res = [(test_list[idx], test_list[j]) for idx in range(len(test_list)) 
                               for j in range(idx + 1, len(test_list)) 
                          if sum((test_list[idx], test_list[j])) == K] 
  
# printing result  
print("The paired tuples equal to K  : " + str(res))  

Output :

The original list is : [3, 4, 0, 5, 2]
The paired tuples equal to K  : [(3, 4), (5, 2)]

Method #2 : Using combinations() + sum()
The combination of above functions can be used to solve this problem. In this combination() is used to form pairs equal to K.

# Python3 code to demonstrate working of  
# Construct Sum pairs equal to K 
# Using combinations() + sum() 
from itertools import combinations 
  
# initializing list 
test_list = [3, 4, 0, 5, 2] 
  
# printing original list 
print("The original list is : " + str(test_list)) 
  
# initializing K 
K = 7
  
# Construct Sum pairs equal to K 
# Using combinations() + sum() 
res = [ele for ele in combinations(test_list, 2) if sum(ele) == K] 
  
# printing result  
print("The paired tuples equal to K  : " + str(res))  

Output :

The original list is : [3, 4, 0, 5, 2]
The paired tuples equal to K  : [(3, 4), (5, 2)]

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