Smallest substring with given string ( Optimized approach )

2.cpp

// Very good problem. But difficult to understand.
// http://leetcode.com/2010/11/finding-minimum-window-in-s-which.html

int search(vector<string> txt, vector<string> pat, string s1, string s2){
    for(int i=0; i<s2.length(); i++) pat[(int)(s2[i])]++;
    txt[256] = {0};
    int begin = 0, end = 0;
    while(end < s1.length()){
      if(pat[s1[end]] == 0) continue;
      txt[s1[end]]++l;
      if(txt[s1[end]] < pat[s1[end]]) cnt++;
      if(cnt == s1.length()){
        while(pat[s1[begin]] == 0 || txt[s1[begin]] > pat[s1[begin]]){
            if(txt[s1[begin]] > pat[s1[begin]]) begin--;
            begin++;
        }
        max_len = max(max_len, (end - begin + 1));
      }
    }
    return max_len;
}