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Smallest Window in a String

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

Given two strings `s` and `t`, find the minimum window substring of `s` that contains all the characters of `t` (including duplicates). If there is no such substring, return an empty string "".

Example 1
    

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

  • Output: "BANC"
    • 

  • Explanation: 
      

    • Step 1: We need to find the smallest substring in s that contains all characters in t.
      • 

    • Step 2: We can use a sliding window approach to track the characters we need.
      • 

    • Step 3: After checking all possible windows, "BANC" is the smallest substring that contains all characters in t (A, B, and C).
      • 

    • Step 4: There is no smaller window that contains all the characters of t.
      • 

    

    •
Example 2
    

  • Input: s = "aaaaaaaaaaaabbbbbcdd", t = "abcdd"
    • 

  • Output: "abbbbbcdd"
    • 

  • Explanation: 
      

    • Step 1: We need to find the smallest substring in s that contains all characters in t.
      • 

    • Step 2: We can use a sliding window approach to track the characters we need.
      • 

    • Step 3: After checking all possible windows, "abbbbbcdd" is the smallest substring that contains all characters in t (a, b, c, d, d).
      • 

    • Step 4: There is no smaller window that contains all the characters of t.
      • 

    

    •
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), where n is the length of string s.
    • 

  • Space Complexity: O(k), where k is the size of the character set.
    •
Hash MapPointers and ReferencesGoogleTech Mahindra
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Hint
Solution

Solution Hints

    
    
  • Use the sliding window technique with two pointers.
    • 
    
  • Use a hash table to keep track of the characters needed from t.
    • 
    
  • Expand the right pointer until all characters of t are found.
    • 
    
  • Contract the left pointer to minimize the window size while maintaining all characters of t.
    • 
    
  • Track the minimum window found so far.
    •

Steps to solve by this approach:

 Step 1: Create hash maps to track character frequencies in string t and the current window

 Step 2: Initialize pointers - left and right - to implement the sliding window technique

 Step 3: Expand the window by moving the right pointer until we find all required characters

 Step 4: Once all required characters are found, try to minimize the window by moving the left pointer

 Step 5: Track the minimum valid window found so far and return it as the result

Submitted Code :