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Minimum Window Substring

Certification: Advanced Level Accuracy: 0% Submissions: 0 Points: 15

Write a C++ program to solve the Minimum Window Substring problem. Given two strings `s` and `t`, return the minimum window substring of `s` that contains all characters of `t` (including duplicates) in any order. If there is no such substring, return the empty string `""`.

Example 1
    

  • Input: s = "ADOBECODEBANC", t = "ABC"
    • 

  • Output: "BANC"
    • 

  • Explanation: 
      

    • Step 1: Create a frequency map of characters in string t.
      • 

    • Step 2: Use a sliding window approach on string s to find windows containing all characters from t.
      • 

    • Step 3: Keep track of the minimum valid window found.
      • 

    • Step 4: The minimum window substring "BANC" contains all characters from "ABC".
      • 

    •
Example 2
    

  • Input: s = "a", t = "a"
    • 

  • Output: "a"
    • 

  • Explanation: 
      

    • Step 1: Create a frequency map of characters in string t.
      • 

    • Step 2: Use a sliding window approach on string s to find windows containing all characters from t.
      • 

    • Step 3: The entire string "a" already contains all characters from t.
      • 

    • Step 4: Return "a" as the minimum window substring.
      • 

    •
Constraints
    

  • 1 ≤ s.length, t.length ≤ 10^5
    • 

  • s and t consist of uppercase and lowercase English letters
    • 

  • The answer is guaranteed to be unique
    • 

  • Time Complexity: O(n + m) where n is the length of s and m is the length of t
    • 

  • Space Complexity: O(k) where k is the size of the character set
    •
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Hint
Solution

Solution Hints

    
  
  • Use the sliding window technique with two pointers
    • 
  
  • Maintain a frequency map of characters in t
    • 
  
  • Expand the right pointer until all required characters are found
    • 
  
  • Contract the left pointer to minimize the window size
    • 
  
  • Keep track of the minimum valid window found so far
    •

Steps to solve by this approach:

 Step 1: Create a frequency map for characters in string t.
 Step 2: Initialize two pointers (left and right) defining the sliding window.
 Step 3: Move the right pointer to expand the window until it contains all characters of t.
 Step 4: Once all required characters are found, move the left pointer to contract the window.
 Step 5: Update the minimum window length whenever a valid window is found.
 Step 6: When the left pointer moves, update character counts and required status.
 Step 7: Return the substring corresponding to the minimum window found.

Submitted Code :