题解 | #字符流中第一个不重复的字符#

使用indexOf

//import java.util.*;

public class Solution {
    //Insert one char from stringstream
    int i = 0;
    StringBuilder sb = new StringBuilder();
   
    public void Insert(char ch){
        sb.append(ch);
    }
  //return the first appearence once char in current stringstream
    public char FirstAppearingOnce(){
        while(i < sb.length() && sb.indexOf("" + sb.charAt(i)) != sb.lastIndexOf("" + sb.charAt(i))) i++;
        return i < sb.length() ? sb.charAt(i) : '#';
    }
}