0076-minimum-window-substring.java

class Solution {

    //sliding window
    public String minWindow(String s, String t) {
        HashMap<Character, Integer> map = new HashMap<>();

        for (char x : t.toCharArray()) {
            map.put(x, map.getOrDefault(x, 0) + 1);
        }

        int matched = 0;
        int start = 0;
        int minLen = s.length() + 1;
        int subStr = 0;
        for (int endWindow = 0; endWindow < s.length(); endWindow++) {
            char right = s.charAt(endWindow);
            if (map.containsKey(right)) {
                map.put(right, map.get(right) - 1);
                if (map.get(right) == 0) matched++;
            }

            while (matched == map.size()) {
                if (minLen > endWindow - start + 1) {
                    minLen = endWindow - start + 1;
                    subStr = start;
                }
                char deleted = s.charAt(start++);
                if (map.containsKey(deleted)) {
                    if (map.get(deleted) == 0) matched--;
                    map.put(deleted, map.get(deleted) + 1);
                }
            }
        }
        return minLen > s.length() ? "" : s.substring(subStr, subStr + minLen);
    }
}