‘substring’ problems solving template

I got the template from the link below:

Here is a 10-line template that can solve most 'substring' problems - LeetCode Discuss

It is related to problem

76. Minimum Window Substring

For most substring problem, we are given a string and need to find a substring of it which satisfy some restrictions. A general way is to use a hashmap assisted with two pointers. The template is given below.

int findSubstring(string s){
        vector<int> map(128,0);
        int counter; // check whether the substring is valid
        int begin=0, end=0; //two pointers, one point to tail and one  head
        int d; //the length of substring
        for() { /* initialize the hash map here */ }
        while(end<s.size()){
            if(map[s[end++]]-- ?){  /* modify counter here */ }
            while(/* counter condition */){ 
                 
                 /* update d here if finding minimum*/
                //increase begin to make it invalid/valid again
                
                if(map[s[begin++]]++ ?){ /*modify counter here*/ }
            }  
            /* update d here if finding maximum*/
        }
        return d;
  }