Minimum window substring

Minimum window substring.cpp

*/
  
   Minimum Window Substring
Hard

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Given two strings s and t of lengths m and n respectively, 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 "".

The testcases will be generated such that the answer is unique.

A substring is a contiguous sequence of characters within the string.

 

Example 1:

Input: s = "ADOBECODEBANC", t = "ABC"
Output: "BANC"
Explanation: The minimum window substring "BANC" includes 'A', 'B', and 'C' from string t.
Example 2:

Input: s = "a", t = "a"
Output: "a"
Explanation: The entire string s is the minimum window.
Example 3:

Input: s = "a", t = "aa"
Output: ""
Explanation: Both 'a's from t must be included in the window.
Since the largest window of s only has one 'a', return empty string.
  */
  
  string minWindow(string s, string t) {
        vector<int> map(128,0);
        for(auto c: t) map[c]++;
        int counter=t.size(), begin=0, end=0, d=INT_MAX, head=0;
        while(end<s.size()){
            if(map[s[end++]]-->0) counter--; //in t
            while(counter==0){ //valid
                if(end-begin<d)  d=end-(head=begin);
                if(map[s[begin++]]++==0) counter++;  //make it invalid
            }  
        }
        return d==INT_MAX? "":s.substr(head, d);
    }