//找到字符流中第一个只出现一次的字符
//构建哈希表，用字符的ASCII码做下标，数值就是该字符在字符流中的位置，如果出现多次，那么这个数值就改成一个负值-2

#include <iostream>
#include<limits>
using namespace std;

class CharStatistics{
public:
    CharStatistics():index(0)//下标初始值0
    {
        for(int i=0;i<256;i++)
            occurence[i]=-1;//初始化哈希表
    }
    void Insert(char ch){
        if(occurence[ch]==-1)
            occurence[ch]=index;
        else if(occurence[ch]>=0)
            occurence[ch]=-2;//不止出现一次
        index++;
    }
    char FirstAppearingOnce(){
        char ch='\0';
        int minIndex=numeric_limits<int>::max();//int可以表示的最大值

        for(int i=0;i<256;i++){
            if(occurence[i]>=0 && occurence[i]<minIndex){//第一个只出现一次
                 minIndex=occurence[i];
                 ch=(char)i;

            }

        }
        return ch;
    }
private:
    //occurence[i]:A character with ASCII value i;
    //occurence[i]=-1: the character has not been found;
    //occurence[i]=-2: the character has been found with multiple times
    //occurence[i]>=0: the character has been found once
    int occurence[256];//ASCII码有 256 个,一个字节8位
    int index;
};
int main()
{
    CharStatistics test;
    test.Insert('g');
    cout<<test.FirstAppearingOnce();
    cout<<endl;
    test.Insert('o');
    test.Insert('o');
    test.Insert('g');
    test.Insert('l');
    test.Insert('e');
     cout<<test.FirstAppearingOnce();
    cout<<endl;
    return 0;
}