Min_window_substring.java

import java.util.HashMap;

public class Min_window_substring {
    public static void main(String[] args) {
   String s1 = "timetopractice";
   String s2 = "toc";
   String s = solutions(s1,s2);
   System.out.println(s);
    }
    static String solutions(String s1, String s2){
        String ans = " " ;
        HashMap<Character,Integer> map2 = new HashMap<>();
        for (int i = 0;  i< s2.length(); i++) {
            char ch = s2.charAt(i);
            map2.put(ch, map2.getOrDefault(ch,0) + 1);
        }

        int mct = 0;
        int dmct = s2.length();

        HashMap<Character,Integer> map1 = new HashMap<>();
        int i =-1;
        int j=-1;

        while(true){
            boolean f1 = false;
            boolean f2 = false;
            //acquire
            while (i < s1.length()-1 && mct<dmct){
                i++;
                char ch = s1.charAt(i);
                map1.put(ch,map1.getOrDefault(ch,0)+1);

                if (map1.getOrDefault(ch,0) <= map2.getOrDefault(ch,0)){
                    mct++;
                }
                f1 = true;
            }
            // collect answers and release
            while (j < i && mct <= dmct){
                String pans = s1.substring(j+1,i+1);
                if(ans.length() == 0 && pans.length() < ans.length()){
                    ans = pans;
                }
                j++;
                char ch = s1.charAt(j);
                if (map1.get(ch) == 1){
                    map1.remove(ch);
                }else {
                    map1.put(ch,map1.get(ch)-1);
                }
                if (map1.getOrDefault(ch,0) < map2.getOrDefault(ch,0)){
                    mct--;
                }
                f2 = true;

                }
            if (f1==false && f2==false){
                break;
            }

        }

        return  ans;
    }

}