给定一个字符串，找到包含该字符串所有字符的最短子串

class Solution {
  String getShortestSubString(String str) {
    if (str == null || str.length() <= 1) {
      return str;
    }
    // 记录目标字符串的起始索引
    int start = 0, end = str.length() - 1;
    // 记录目标字符串的开始位置
    int pStart = 0;
    Map<Character, List<Integer>> map = new HashMap<Character, List<Integer>>();
    for (int index = 0; index < str.length(); index++) {
      map.put(str.charAt(index), null);
    }
    int remainingCharacter = map.keySet().size();
    for (int i = 0; i < str.length(); i++) {
      char c = str.charAt(i);
      if (map.get(c) == null) {
        List list = new LinkedList<Integer>();
        map.put(c, list);
        remainingCharacter--;
      }
      map.get(c).add(i);
      while (map.get(str.charAt(pStart)).size() > 1) {
        map.get(str.charAt(pStart)).remove(0);
        pStart++;
      }
      if (remainingCharacter == 0) {
        if (i - pStart < end - start) {

          start = pStart;
          end = i;
        }
      }
    }
    return str.substring(start, end + 1);
  }
}
class TestSolution {
  @Test
  public void testGetShortestSubString() {
    Solution solution = new Solution();
    Assert.assertEquals("dbccaaabcefg", solution.getShortestSubString("abcddbccaaabcefggf"));
  }
}