public static void main(String[] strs) {

System.out.println(MinimumWindowSubString.minWindow("a", "a"));

}

public static String minWindow(String S, String T) {

if (S == null || T == null || T.length() == 0 || S.length() == 0) {

return "";

}

int resultLen = -1;

int resultleft = 0;

int sum = 0;

HashMap<Character, Integer> setSub = new HashMap<Character, Integer>();

for (int i = 0; i < T.length(); i++) {

if (setSub.containsKey(T.charAt(i))) {

setSub.put(T.charAt(i), setSub.get(T.charAt(i)) + 1);

} else {

setSub.put(T.charAt(i), 1);

}

}

// count the number of characters in String T;

sum = setSub.size();

HashMap<Character, Integer> map = new HashMap<Character, Integer>();

// record the left board.

int left = 0;

// record the

//int equal = sum;

for (int i = 0; i < S.length(); i++) {

if (setSub.containsKey(S.charAt(i))) {

if (map.containsKey(S.charAt(i))) {

map.put(S.charAt(i), map.get(S.charAt(i)) + 1);

} else {

map.put(S.charAt(i), 1);

}

if (map.get(S.charAt(i)) == setSub.get(S.charAt(i))) {

sum--;

}

}

// contains all the charaters.

if (0 == sum) {

while (true) {

Integer number = map.get(S.charAt(left));

// it should contains at least the number in T

if (number != null && number <= setSub.get(S.charAt(left))) {

map.put(S.charAt(left), number - 1);

sum++;

break;

}

if (number != null) {

map.put(S.charAt(left), number - 1);

}

left++;

}

if (resultLen == -1 || resultLen > i - left + 1) {

resultLen = i - left + 1;

resultleft = left;

left++;

}

}

}

if (resultLen == -1) {

return "";

} else {

return S.substring(resultleft, resultleft + resultLen);

}

}

}