Introduction

In this blog post, we will explore how to solve the LeetCode problem "3045" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

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 <= 105 1 <= words[i].length <= 105 words[i] consists only of lowercase English letters. The sum of the lengths of all words[i] does not exceed 5 * 105.

Explanation

Here's the breakdown of the solution:

• Iterate and Check: The core idea is to iterate through all possible pairs (i, j) where i < j, and for each pair, check if isPrefixAndSuffix(words[i], words[j]) is true.

• Efficient Prefix/Suffix Check: The isPrefixAndSuffix function directly compares prefixes and suffixes of str2 with str1 to determine if str1 satisfies the condition.

• Runtime Complexity: O(n^2 m), where n is the number of words, and m is the maximum length of a word. *Storage Complexity: O(1).

Code

    def countPrefixSuffixPairs(words):
    """
    Counts the number of index pairs (i, j) such that i < j, and isPrefixAndSuffix(words[i], words[j]) is true.
    """

    def isPrefixAndSuffix(str1, str2):
        """
        Checks if str1 is both a prefix and a suffix of str2.
        """
        n1 = len(str1)
        n2 = len(str2)
        if n1 > n2:
            return False
        return str2.startswith(str1) and str2.endswith(str1)

    count = 0
    n = len(words)
    for i in range(n):
        for j in range(i + 1, n):
            if isPrefixAndSuffix(words[i], words[j]):
                count += 1
    return count