Find the longest common sub-string among a set of strings...

substr.py

from collections import defaultdict
from pprint import pprint


class Solution:
    def longestCommonPrefix(self, strs: List[str]) -> str:
        str_count = len(strs)
        min_len = min([len(s) for s in strs])
        print(f"Minimum string length: {min_len:,}")

        if min_len == 0:
            return ""

        print("Indexing strings ...")
        char_index = defaultdict(int)
        for i in range(0, min_len):
            for s in strs:
                char_index[(i, s[i])] += 1

        print(pprint(char_index))

        print("Computing maximum prefix from index ...")
        max_prefixes: list[str] = []
        for i, a_str in enumerate(strs):
            max_prefix = ""
            for j, c in enumerate(a_str):
                print(f"Char {i},{j}: {c}")
                if char_index[(j, c)] != str_count:
                    print(f"Max prefix at end of string '{a_str}': {max_prefix}")
                    break
                else:
                    print(f"Appending '{c}' to max_prefix '{max_prefix}' to get '{max_prefix + c}'")
                    max_prefix += c
            max_prefixes.append(max_prefix)
        return min(max_prefixes)