[leetcode] Minimum Window Substring

public class Solution {
    public String minWindow(String S, String T) {
        if (S == null || T == null)
            return "";

        int[] needToFind = new int[256];
        int[] found = new int[256];

        for (int i = 0; i < T.length(); i++)
            needToFind[T.charAt(i)]++;
        String result = "";
        int begin = 0, end = 0;
        int minWin = Integer.MAX_VALUE;
        int count = 0;

        for (end = 0; end < S.length(); end++) {
            if (needToFind[S.charAt(end)] == 0)
                continue;

            char ch = S.charAt(end);
            found[ch]++;
            if (found[ch] <= needToFind[ch])
                count++;
            
            if (count == T.length()) {
                //move the begin pointer while the constrain meets
                while (begin < S.length()
                        && (found[S.charAt(begin)] > needToFind[S.charAt(begin)] || needToFind[S.charAt(begin)] == 0)) {

                    if (found[S.charAt(begin)] > 0)
                        found[S.charAt(begin)]--;

                    begin++;
                }

                //update the min according to the current window
                if (end - begin + 1 < minWin) {
                    minWin = end - begin + 1;
                    result = S.substring(begin, end + 1);
                }

            }

        }
        return result;

    }

    public static void main(String[] args) {
        System.out.println(new Solution().minWindow("ADOBECODEBANC", "ABC"));

    }

}