Introduction

In this blog post, we will explore how to solve the LeetCode problem "2800" 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

Given three strings a, b, and c, your task is to find a string that has the minimum length and contains all three strings as substrings. If there are multiple such strings, return the lexicographically smallest one. Return a string denoting the answer to the problem. Notes A string a is lexicographically smaller than a string b (of the same length) if in the first position where a and b differ, string a has a letter that appears earlier in the alphabet than the corresponding letter in b. A substring is a contiguous sequence of characters within a string. Example 1: Input: a = "abc", b = "bca", c = "aaa" Output: "aaabca" Explanation: We show that "aaabca" contains all the given strings: a = ans[2...4], b = ans[3..5], c = ans[0..2]. It can be shown that the length of the resulting string would be at least 6 and "aaabca" is the lexicographically smallest one. Example 2: Input: a = "ab", b = "ba", c = "aba" Output: "aba" Explanation: We show that the string "aba" contains all the given strings: a = ans[0..1], b = ans[1..2], c = ans[0..2]. Since the length of c is 3, the length of the resulting string would be at least 3. It can be shown that "aba" is the lexicographically smallest one. Constraints: 1 <= a.length, b.length, c.length <= 100 a, b, c consist only of lowercase English letters.

Explanation

Here's a breakdown of the approach, followed by the Python code:

• Permutations and Overlaps: Generate all 6 permutations of the input strings a, b, and c. For each permutation, try to merge the strings together, minimizing the overlap between them.

• Overlap Calculation: Efficiently calculate the maximum overlap between two strings. The overlap represents the number of characters by which the two strings can be joined to form a shorter string.

• Lexicographical Comparison: Compare the merged strings based on their length and lexicographical order to find the shortest and lexicographically smallest result.

• Runtime and Storage Complexity: O(1) because the input strings have a fixed upper bound in length, and the number of permutations is constant. The storage complexity is O(1) as well due to the input size limitations.

Code

    def solve():
    def find_overlap(s1, s2):
        n1 = len(s1)
        n2 = len(s2)
        overlap = 0
        for i in range(1, min(n1, n2) + 1):
            if s1[n1 - i:] == s2[:i]:
                overlap = i
        return overlap

    def merge_strings(s1, s2):
        overlap = find_overlap(s1, s2)
        return s1 + s2[overlap:]

    def find_shortest_superstring(a, b, c):
        import itertools
        strings = [a, b, c]
        permutations = list(itertools.permutations(strings))

        shortest_string = None

        for p in permutations:
            merged1 = merge_strings(p[0], p[1])
            merged2 = merge_strings(merged1, p[2])

            if shortest_string is None or len(merged2) < len(shortest_string) or \
               (len(merged2) == len(shortest_string) and merged2 < shortest_string):
                shortest_string = merged2

        return shortest_string

    a = input()
    b = input()
    c = input()
    print(find_shortest_superstring(a, b, c))
solve()