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"。
方法一：
class Solution {
public:
Solution(): index(0) {
for (int i = 0; i < 256; ++i) {
occurrence[i] = -1;
}
}
//Insert one char from stringstream
void Insert(char ch) {
if (occurrence[ch] == -1) {
occurrence[ch] = index;
}
else {
occurrence[ch] = -2;
}
++index;
}
//return the first appearence once char in current stringstream
char FirstAppearingOnce() {
char ch = '#';
int minIndex = INT_MAX;
for (int i = 0; i < 256; ++i) {
if (occurrence[i] >= 0 && occurrence[i] < minIndex) {
minIndex = occurrence[i];
ch = i;
}
}
return ch;
}
private:
int occurrence[256];
int index;
};
方法二：
class Solution
{
public:
//Insert one char from stringstream
void Insert(char ch)
{
++hashArray[ch-'\0'];
if( hashArray[ch-'\0'] == 1){
data.push_back(ch);
}
}
//return the first appearence once char in current stringstream
char FirstAppearingOnce()
{
while( !data.empty() && hashArray[data.front()] >= 2 ){
data.pop_front();
}
if( data.empty() )
return '#';
return data.front();
}
private:
unsigned char hashArray[128];
deque<char> data;
};
