Get Twin Primes as output from an inputted list

Question

I want to enter numbers separated by spaces as input and store them in a list. I want to get all twin primes in that list as output. If there’s no any twin primes in that inputted numbers I want to have an output "No any twin primes".

Twin Prime – two prime numbers whose difference is 2

So my code was like this:

lst = input()
test_list =[]

for ele in lst.split():
    n_int = int(ele)
    test_list.append(n_int)

def prime(x):
    for k in range(2, x):
        if x%k == 0:
            return False
    return True

diff = 0
for i in test_list:
    for j in test_list:
        if prime(i) and prime(j):
            diff = abs(i-j)
        if diff == 2:
            print(i, j)
        
print("No any twin primes")

If I input a number series like 3 4 5 7 8, I expect an output

3 5
5 7

but my output was

3 5
5 3
5 4
5 7
5 9
7 5
No any twin primes

If there’s no any twin primes in the inputted list (2 3 7 9) I get my expected output as

No any twin primes

.

Asked By: Se00

||

Source

Answer 1

Changes made:

(1) Created a res as a list which stores the Twin primes

(2) iteration of inner for loop is from i+1 to end

Code:-

lst = input("Enter the numbers: ")
test_list =[]

for ele in lst.split():
    n_int = int(ele)
    test_list.append(n_int)

def prime(x):
    for k in range(2, x):
        if x%k == 0:
            return False
    return True

diff = 0
res=[]
for i in range(len(test_list)):
    for j in range(i+1,len(test_list)):
        if prime(test_list[i]) and prime(test_list[j]):
            diff = abs(test_list[i]-test_list[j])
            if diff == 2:
                res.append([test_list[i],test_list[j]])
if res: 
    for i,j in res:
        print(i,j)
else:
    print("No any twin primes")

Output:-

Enter the numbers: 3 4 5 7 8
3 5
5 7

Enter the numbers: 2 3 7 9
No any twin primes

Answered By: Yash Mehta

Answer 2

Here’s my try:

def twinPrimes(iter):
    primes = []
    res = []
    for i in iter:
        for j in range(2, int(i/2)+1):
            if i % j == 0:
                break
        else:
            primes.append(i)
    for i in range(len(primes)-1):
        if primes[i+1] - 2 == primes[i]:
            res.append((primes[i], primes[i+1]))
    if res == []:
        return "No any twin primes"
    else:
        return res
print(twinPrimes([3,5,7]))

You can also change the return to printing like:

def twinPrimes(iter):
    primes = []
    res = []
    for i in iter:
        for j in range(2, int(i/2)+1):
            if i % j == 0:
                break
        else:
            primes.append(i)
    for i in range(len(primes)-1):
        if primes[i+1] - 2 == primes[i]:
            res.append((primes[i], primes[i+1]))
            print(primes[i], primes[i+1])
    if res == []:
        print("No any twin primes")

Input: twinPrimes([3,5,7])
Output:

3 5
5 7

Input: twinPrimes([2,5,9])
Output:

No any twin primes

Answered By: The Myth

Get Twin Primes as output from an inputted list

Question:

Answers: