Minimum Window Substring

Given a string S and a string T, find the minimum window in S which would contain all the characters in T in complexity O (n ).

For example,
S ="ADOBECODEBANC"
T ="ABC"

Minimum window is "BANC" .

Note:
If There is no such window in S, this covers all characters in T, return the empty string "" .

If There is multiple such windows, you is guaranteed that there would always being only one unique minimum window in S.

classSolution { Public:    stringMinwindow (stringSstringt) {unordered_map<Char,int>m;  for(Charc:t) {M[c]++; }        intSL =s.length (); intCounter =t.length (); intStart =0, end =0; intMinstart =0, Minlen =Int_max;  while(End <SL) {            if(m[s[end]]>0) {counter--; } M[s[end]]--; End++;  while(Counter = =0){                if(End-start <Minlen) {Minstart=start; Minlen= end-start; } M[s[start]]++; if(m[s[start++]) >0) {counter++; }            }        }        if(Minlen <Int_max)returns.substr (Minstart,minlen); Else            return ""; }};

Minimum Window Substring