Input: s = "ADOBECODEBANC", t = "ABC" Output: "BANC" Explanation: The minimum window substring of string s that contains all characters of string t is "BANC".

Input: s = "a", t = "a" Output: "a" Explanation: The entire string is the minimum window that contains all characters of the target.

Disclaimer: Here is the practice link to help you assess your knowledge better. It's highly recommend trying to solve it before looking at the solution.

Brute Force Approach

Algorithm

We are given two strings: a source string and a target string. The goal is to find the smallest possible window (substring) in the source that contains all the characters of the target string, including duplicates. A brute-force solution would be to consider every possible substring of the source string, and for each substring, check if it contains all characters of the target string with the correct frequencies.

To check if a substring is valid, we need to compare the frequency of each character in the substring with the required frequency from the target string. If the current substring satisfies the condition, we update the minimum length and store the substring. After checking all possible substrings, the one with the minimum valid length will be the answer. This approach is inefficient for large strings.

Generate all possible substrings of the source string.
For each substring, count the characters and compare the frequency with that of the target string.
If the substring satisfies the required frequency for all characters, check if its length is smaller than the current minimum.
If yes, update the minimum window and store the current substring as the result.
After all substrings are checked, return the minimum valid substring. If no such substring is found, return an empty string.