1class Solution {2    public String minWindow(String s, String t) {3        if (t.isEmpty()) return "";4        int[] need = new int[128];5        for (char c : t.toCharArray()) need[c]++;6        int left = 0, missing = t.length(), bestStart = 0, bestLen = Integer.MAX_VALUE;7        for (int right = 0; right < s.length(); right++) {8            char c = s.charAt(right);9            if (need[c] > 0) missing--;10            need[c]--;11            while (missing == 0) {12                if (right - left + 1 < bestLen) {13                    bestStart = left; bestLen = right - left + 1;14                }15                char removed = s.charAt(left++);16                need[removed]++;17                if (need[removed] > 0) missing++;18            }19        }20        return bestLen == Integer.MAX_VALUE ? "" : s.substring(bestStart, bestStart + bestLen);21    }22}