题解 | #字符流中第一个不重复的字符# Java 直接用 LinkedHashSet 解决

public class Solution {
  LinkedHashSet<Character> set = new LinkedHashSet<>();

  //Insert one char from stringstream
  public void Insert(char ch) {
    if (set.contains(ch))
      set.remove(ch);
    else
      set.add(ch);
  }

  //return the first appearence once char in current stringstream
  public char FirstAppearingOnce() {
    if (set.isEmpty()) return '#';
    return set.iterator().next();
  }
}