Trying to integrate gcd function

[hhydration]

I have this function, it prints a list of values.

def kasinski(text):
    trigraphs=[]
    distances=[]
    for trigraph in range (len(text)-2):
        newtrigraph= text[trigraph:trigraph+3]
        if newtrigraph in trigraphs:
            distances.append(trigraph-(text.index(newtrigraph)))
        else:
            trigraphs.append(newtrigraph)
            trigraphs.append(trigraph)
            return distances

I also have functions that will find the greatest common divisor of all numbers in a list

def gcd(x,y):
    if y==0:
        return x
    else:
        return gcd(y, x% y)
def gcd_list_helper(list, index:
    if index==len((list)-1):
        return list[index]
    else:
        return gcd(list[index], gcd_list_helper(list, index+1))
def gcd_of_list(list):
    return gcd_list_helper(list, 0)

I am having trouble integrating the gcd function into my first function so that the kasiski function returns the GCD of the list rather than the list. Any pointers?