Identifying Pattern Substrings — Problem Statement & Solution Guide
Problem Description
Given a string and a pattern, find the length of the longest substring that occurs at least twice in the string and also contains the given pattern as a substring.
Examples
Input
string = 'abcabcabcabc', pattern = 'abc'
Output
4
Explanation: Step-by-step: 1. Find all substrings of the string. 2. Filter out substrings that do not contain the pattern. 3. Find the longest substring that occurs at least twice in the string and also contains the given pattern as a substring.
Input
string = 'ababab', pattern = 'ab'
Output
6
Explanation: Step-by-step: 1. Find all substrings of the string. 2. Filter out substrings that do not contain the pattern. 3. Find the longest substring that occurs at least twice in the string and also contains the given pattern as a substring.
Constraints
- The length of the input string is at most 1000 characters.
- The length of the pattern is at least 1 character and at most 100 characters.
- The input string and pattern only contain lowercase English letters.
Optimal Approach & Strategy
The optimal approach involves using a hashmap to store the frequency of each substring and a sliding window to generate substrings, reducing the time complexity to O(n^2).
Brute Force Approach
A naive approach is to generate all possible substrings of the input string and check each one to see if it contains the given pattern and occurs at least twice, resulting in a time complexity of O(n^3). This approach is inefficient for large strings.
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