题目:请实现一个函数用来找出字符流中第一个只出现一次的字符。例如,当从字符流中只读出前两个字符"go"时,第一个只出现一次的字符是'g'。当从该字符流中读出前六个字符"google"时,第一个只出现一次的字符是'l'。
//哈希表
class CharStatistics
{
public:
CharStatistics() :index(0)
{
for (int i = 0;i < 256;++i)
occurrence[i] = -1;
}
void insert(char ch)
{
if (occurrence[ch] == -1)
occurrence[ch] = index;
else if (occurrence[ch] >= 0)
occurrence[ch] = -2;
++index;
}
char FirstAppearingOnce()
{
char ch = '\0';
int minIndex = numeric_limits<int>::max();
for (int i = 0;i < 256;++i)
{
if (occurrence[i] >= 0 && occurrence[i] < minIndex)
{
ch = (char)i;
minIndex = occurrence[i];
}
}
return ch;
}
private:
int occurrence[256];
int index;
};