Minimum Window Substring | Leetcode #76

class Solution {
    #define SIZE 256+2
    bool equalFreq(vector<int>& curr,vector<int>& freq){//Check frequency of current window with freq(t)
        for(int i=0;i<SIZE;++i)
            if(freq[i]>0 and curr[i]<freq[i])
                return false;
        return true;
    }
public:
    string minWindow(string s, string t) {
        int n=s.size();
        if(n<t.size())
            return "";

        vector<int> freq(SIZE,0);
        for(char &c: t)//Find freq(t)
            freq[c]++;

        int l=0,r=0;//left and right pointers of sliding window
        int minWin = INT_MAX;
        string ans="";
        vector<int> curr(SIZE,0);
        
        while(r<n){ //run till end of string
            curr[s[r]]++;
            if(equalFreq(curr,freq)){//If we have all chars of t in our curr window
                do {    //move left ptr to as right as possible to minimize window size
                    curr[s[l]]--;
                    l++;
                }while(equalFreq(curr,freq));//Run until curr no more matches t
                if(minWin > r-l+2){//If curr window size is less than already know minWin size
                    minWin = r-l+2;
                    ans = s.substr(l-1,minWin);
                }
            }
            r++;
        }
        return ans;
    }
};