字符流中第一个不重复的字符

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;

};

推荐阅读更多精彩内容