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Minimum Window Substring

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

Write a C program to find the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such window in s that covers all characters in t, return the empty string "". If there are multiple valid windows, return the one with the smallest length.

Example 1
    
  
  • Input: s = "ADOBECODEBANC", t = "ABC"
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  • Output: "BANC"
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  • Explanation: 
    
      
      
    • Step 1: The minimum window substring "BANC" includes one 'A', one 'B', and one 'C' from string t.
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    • Step 2: This is the shortest substring that contains all characters of t.
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    • Step 3: Therefore, the answer is "BANC".
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Example 2
    
  
  • Input: s = "a", t = "aa"
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  • Output: ""
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  • Explanation: 
    
      
      
    • Step 1: String t requires two 'a' characters.
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    • Step 2: String s only contains one 'a' character.
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    • Step 3: Therefore, no valid window exists, return empty string.
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Constraints
    
  
  • 1 ≤ s.length, t.length ≤ 10^5
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  • s and t consist of uppercase and lowercase English letters
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  • Time Complexity: O(|s| + |t|)
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  • Space Complexity: O(|s| + |t|)
    •
AlgorithmsHCL TechnologiesApple
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Hint
Solution

Solution Hints

    
  
  • Use sliding window technique with two pointers (left and right).
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  • Maintain frequency count of characters in t using a hash map.
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  • Expand window by moving right pointer until all characters of t are covered.
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  • Contract window by moving left pointer while maintaining validity.
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  • Keep track of minimum window length and starting position.
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  • Use a counter to track how many unique characters are fully matched.
    •

Steps to solve by this approach:

 Step 1: Create frequency map for all characters in string t and count unique characters needed.
 Step 2: Use two pointers (left and right) to create a sliding window over string s.
 Step 3: Expand window by moving right pointer and update character frequencies.
 Step 4: When window contains all required characters, try to contract from left.
 Step 5: While contracting, keep track of the minimum valid window found.
 Step 6: Remove character from left side and update frequencies and validity counter.
 Step 7: Continue until right pointer reaches end, then return the minimum window found.

Submitted Code :