[jobdu]第一个只出现一次的字符

刚开始还在想双指针，完全没必要。然后最土的可以扫两遍O(n)，用一个数组记录出现次数。然后想到如果数组里记录出现的位置，可以只扫一遍O(n)，第二遍扫字符集就行了。

#include <iostream>

#include <string>

using namespace std;

 

#define INF 1<<30

int main()

{

    string s;

    while (cin >> s)

    {

        int len = s.length();

        if (len == 0)

        {

            cout << "-1" << endl;

            continue;

        }

        int count[26];

        for (int i = 0; i < 26; i++)

        {

            count[i] = -1;

        }

        for (int i = 0; i < len; i++)

        {

            if (count[s[i]-'A'] == -1)

            {

                count[s[i]-'A'] = i; // save the first position

            }

            else

            {

                count[s[i]-'A'] = INF;

            }

        }

        int min = INF;

        for (int i = 0; i < 26; i++)

        {

            if (min > count[i] && count[i] != -1) min = count[i];

        }

        if (min != INF) cout << min << endl;

        else cout << -1 << endl;

    }

    return 0;

}