# general computation of an overlap function
def overlap_function(pattern):
    ol_list = [0] * len(pattern)

    pos = 1  # first is always zero
    while (pos < len(pattern)):
        ol_prev = ol_list[pos - 1]

        if pattern[pos] == pattern[ol_prev]:
            ol_list[pos] = ol_prev + 1
        else:
            found = False
            j = ol_prev
            curr_overlap = ol_prev
            while not found and j >= 1:
                # try extend a smaller prefix - based on pattern [ol[pos-1]]
                if pattern[pos] == pattern[j]:
                    found = True
                    ol_list[pos] = curr_overlap + 1
                else:
                    curr_overlap = ol_list[j-1]
                    j = ol_list[j-1]

            if not found:  # compare with the first
                if pattern[pos] == pattern[0]:
                    ol_list[pos] = 1
        pos += 1
    return ol_list

if __name__ == '__main__':
    ol_list = overlap_function('catcapcatcarcatcapcatcat')
    print (ol_list)