76. Minimum Window Substring

class Solution {
    public String minWindow(String s, String t) {
        if (s == null || s.length() == 0) return "";
        int lo = 0, hi = 0;
        int minLen = Integer.MAX_VALUE;
        int minStart = -1, minEnd = -1;

        int[] map = new int[128];
        for (char c : t.toCharArray()) {
            map[c]++;
        }

        int count = 0;
        for (hi = 0; hi < s.length(); hi++) {
            if (map[s.charAt(hi)] > 0) {
                count++;
            }
            map[s.charAt(hi)]--;
            if (count == t.length()) {
                while (lo < hi && map[s.charAt(lo)] < 0) {
                    map[s.charAt(lo)]++;
                    lo++;
                }

                if (hi - lo + 1 < minLen) {
                    minLen = hi - lo + 1;
                    minStart = lo;
                    minEnd = hi + 1;
                }
                map[s.charAt(lo)]++;
                count--;
                lo++;
            }
        }

        return (minStart == -1) ? "" : s.substring(minStart, minEnd);
    }
}