字符流中第一个不重复的字符

//可以申请一个256大小的数组来实现一个简易的哈希表。时间复杂度为O(n)，空间复杂度O(n).

public class Solution {
    private int[] hash = new int[256];
    StringBuffer s = new StringBuffer();
    //Insert one char from stringstream
    public void Insert(char ch)
    {
        s.append(ch);
        hash[ch] += 1;
    }
  //return the first appearence once char in current stringstream
    public char FirstAppearingOnce()
    {
        for(int i = 0; i<s.length(); i++) {
            if(hash[s.charAt(i)] == 1) return s.charAt(i);
        }
        return ‘#‘;
    }
}