Can you help me improve this Python code?

Question

Given a list of numbers and a number k, return whether any two numbers from the list add up to k. For example, given [10, 15, 3, 7] and k of 17, return true since 10 + 7 is 17

This is the code I came up with :

alist=[1,3,5,6,9]
check=False
k=int(input("Enter a number : "))
for i in range(5):
for j in range(5):
if((alist[i]+alist[j])==k):
print(alist[i],"+",alist[j],"=",k)
check=True
if check!=True:
print("Numbers dont add up")
else :
print("Therefore numbers add up")

The code is running fine, but if I enter the value of k as 10, this is what I get as output :
Enter a number : 10
1+9=10
5+5=10
9+1=10

Notice that 5 is repeated twice, which should not happen. A number should be used only once. I could add this condition while alist[i]!=alist[j]

But is there a better way to write this code?

Answer 1

One thing I would do would be to change the range you have set for your for loops. Just to make it a bit more dynamic, you can set the first for loop to have a range of len(alist) so that it loops through the entirety of the list, no matter its size. For the inner loop, instead of having it loop through every single element in that list, you could have it loop through every element ahead of it (ex. The first iteration would check if 1 + 3 = 10, 1 + 5 = 10, and so forth, the second would check if 3 + 5 = 10, 3 + 6 = 10, and so forth). All you would need to do to do that is set the range to range(i+1, len(alist)) to loop through everything correctly.

Answer 2

#i have this try :)
alist=[1,3,5,6,9]
check=False
k=int(input("Enter a number : "))
for i in alist:
for j in alist:
if(i != j and i+j==k):
print(i,"+",j,"=",k)
if(check==False):
print("Numbers dont add up")
else:
print("Therefore numbers add up")

Answer 3

Thanks Faisal and Sousou

Answer 4

My implimentation is based on simplicity. Hope you like it🙂

# my implementation
alist = [1,3,5,6,9]
check = False
k = int(input("Enter a number: "))
result = 0
second = 0
for i in alist:
result = k - i
if result in alist and result != i:
check = True
second = i
break

if check == False:
print("Numbers dont add up")

else:
print(f"{second} + {result} = {k}")

Answer 5

Thanks Thomas. Thats a nice approach to the problem👍👍