Count Prefix and Suffix Pairs I.py

'''
You are given a 0-indexed string array words.

Let's define a boolean function isPrefixAndSuffix that takes two strings, str1 and str2:

isPrefixAndSuffix(str1, str2) returns true if str1 is both a 
prefix
 and a 
suffix
 of str2, and false otherwise.
For example, isPrefixAndSuffix("aba", "ababa") is true because "aba" is a prefix of "ababa" and also a suffix, but isPrefixAndSuffix("abc", "abcd") is false.

Return an integer denoting the number of index pairs (i, j) such that i < j, and isPrefixAndSuffix(words[i], words[j]) is true.

'''

class Solution:
    def countPrefixSuffixPairs(self, words: List[str]) -> int:
        def helper(w1,w2):
            return w2.startswith(w1) and w2.endswith(w1)

        n =len(words)
        res = 0
        for i in range(n):
            for j in range(n):
                if i!=j and i<j and helper(words[i],words[j]):
                    res+=1
        return res