3042 - Count Prefix and Suffix Pairs I\.

Easy

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.

Example 1:

Input: words = "a","aba","ababa","aa"

Output: 4

Explanation: In this example, the counted index pairs are:

i = 0 and j = 1 because isPrefixAndSuffix("a", "aba") is true.

i = 0 and j = 2 because isPrefixAndSuffix("a", "ababa") is true.

i = 0 and j = 3 because isPrefixAndSuffix("a", "aa") is true.

i = 1 and j = 2 because isPrefixAndSuffix("aba", "ababa") is true.

Therefore, the answer is 4.

Example 2:

Input: words = "pa","papa","ma","mama"

Output: 2

Explanation: In this example, the counted index pairs are:

i = 0 and j = 1 because isPrefixAndSuffix("pa", "papa") is true.

i = 2 and j = 3 because isPrefixAndSuffix("ma", "mama") is true.

Therefore, the answer is 2.

Example 3:

Input: words = "abab","ab"

Output: 0

Explanation: In this example, the only valid index pair is i = 0 and j = 1, and isPrefixAndSuffix("abab", "ab") is false.

Therefore, the answer is 0.

Constraints:

• 1 <= words.length <= 50

• 1 <= words[i].length <= 10

• words[i] consists only of lowercase English letters.