Minimum Window Substring

class Solution {
public:
    string minWindow(string s, string t) {
        string ans="";

        if(s.size()==0 || t.size()==0)
            return ans;

        if(t.size()>s.size())
            return ans;

        unordered_map<char,pair<int,int>> mp;

        for(int i=0;i<t.size();i++){
            mp[t[i]].first++;
            mp[t[i]].second++;
        }

        int l=0,r=0,len=INT_MAX,dc=0,ansl=0,ansr=0,idc=mp.size();
        char c,cc;

        while(r<s.size()){
            c=s[r];
            mp[c].second--;

            if(mp[c].second==0 && mp[c].first!=0)
                dc++;

            while(dc==idc && l<=r){
                cc=s[l];
                if(len==INT_MAX || len>(r-l+1)){
                    ansl=l;
                    ansr=r;
                    len=(ansr-ansl+1);
                }

                mp[cc].second++;
                if(mp[cc].second>0 && mp[cc].first!=0)
                    dc--;

                l++;
            }
            r++;
        }

        if(len!=INT_MAX){
            for(int i=ansl;i<=ansr;i++){
                ans+=s[i];
            }
        }
        return ans;
    }
};