76. Minimum Window Substring

class Solution {
    public String minWindow(String s, String t) {

        if (s.length() == 0 || t.length() == 0) {
            return "";
        }

        Map<Character, Integer> dictT = new HashMap<Character, Integer>();

        for (int i = 0; i < t.length(); i++) {
            int count = dictT.getOrDefault(t.charAt(i), 0);
            dictT.put(t.charAt(i), count + 1);
        }

        int required = dictT.size();
        
        List<Pair<Integer, Character>> filteredS = new ArrayList<Pair<Integer, Character>>();
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (dictT.containsKey(c)) {
                filteredS.add(new Pair<Integer, Character>(i, c));
            }
        }

        int l = 0, r = 0, formed = 0;
        Map<Character, Integer> windowCounts = new HashMap<Character, Integer>();  
        int[] ans = {-1, 0, 0};

        while (r < filteredS.size()) {
            char c = filteredS.get(r).getValue();
            int count = windowCounts.getOrDefault(c, 0);
            windowCounts.put(c, count + 1);

            if (dictT.containsKey(c) && windowCounts.get(c).intValue() == dictT.get(c).intValue()) {
                formed++;
            }

            while (l <= r && formed == required) {
                c = filteredS.get(l).getValue();

                int end = filteredS.get(r).getKey();
                int start = filteredS.get(l).getKey();
                if (ans[0] == -1 || end - start + 1 < ans[0]) {
                    ans[0] = end - start + 1;
                    ans[1] = start;
                    ans[2] = end;
                }

                windowCounts.put(c, windowCounts.get(c) - 1);
                if (dictT.containsKey(c) && windowCounts.get(c).intValue() < dictT.get(c).intValue()) {
                    formed--;
                }
                l++;
            }
            r++;   
        }
        return ans[0] == -1 ? "" : s.substring(ans[1], ans[2] + 1);
    }
}

Runtime: 17 ms, faster than 25.92% of Java online submissions for Minimum Window Substring.
Memory Usage: 44.5 MB, less than 7.10% of Java online submissions for Minimum Window Substring.