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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 such that every character in t (including duplicates) is included in the window. If there is no such substring, return the empty string "".

Example 1
    
  
  • Input: s = "ADOBECODEBANC", t = "ABC"
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  • Output: "BANC"
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  • Explanation: 
    
      
      
    • The minimum window substring "BANC" includes 'A', 'B', and 'C' from string t.
      • 
    
    
  
    •
Example 2
    
  
  • Input: s = "a", t = "a"
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  • Output: "a"
    • 
  
  • Explanation: 
    
      
      
    • The entire string s is the minimum window.
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    •
Constraints
    
  
  • 1 <= s.length, t.length <= 10^5
    • 
  
  • s and t consist of uppercase and lowercase English letters
    • 
  
  • Time Complexity: O(n)
    • 
  
  • Space Complexity: O(k) where k is the size of the character set
    •
StringsKPMGD. E. Shaw
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Hint
Solution

Solution Hints

    
  
  • Use the sliding window technique to find the minimum window
    • 
  
  • Maintain two frequency maps: one for required characters from t and one for current window
    • 
  
  • Use two pointers to expand or contract the window as needed
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  • Keep track of how many characters from t are currently matched
    •

Steps to solve by this approach:

 Step 1: Create two dictionaries - one to store the frequency of characters in string t and another for the current window.
 Step 2: Initialize two pointers, left and right, starting at the beginning of string s.
 Step 3: Move the right pointer to expand the window until all characters in t are found in the current window.
 Step 4: Once all required characters are found, move the left pointer to contract the window while maintaining the requirement.
 Step 5: During contraction, update the minimum window length if a smaller valid window is found.
 Step 6: Continue expanding and contracting until the right pointer reaches the end of string s.
 Step 7: Return the minimum window substring found, or an empty string if no valid window exists.

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