惭愧，使用了双重循环。

#include <iostream>
#include <string>
#include <vector>
#include <map>
#include <unordered_map>

using namespace std;

string getfilename(string& str)
{
    auto pos = str.find_last_of("\\");
    str = str.substr(pos + 1);
    pos = str.find(" ");
    if (pos > 16)
    {
        str = str.substr(pos - 16);
    }
    return str;
}

int main()
{
    string str;
    unsigned lineNo;
    //string rst[8];
    unsigned cnt = 0;
    pair<string, unsigned> par;
    vector<pair<string, unsigned> > rst;
    //unorder_map<string, unsigned> rst;
    while(getline(cin, str))
    {
        str = getfilename(str);
        bool flag = false;
        for(auto it = rst.begin(); it != rst.end(); ++it)
        {
            if(it->first == str)
            {
                it->second++;
                flag = true;
                break;
            }
        }
        if(!flag)
        {
            rst.push_back({str, 1});
        }

    }
    cnt = 0;
    if(rst.size() > 8)
    {
        cnt = rst.size() - 8;
    }
    for(auto it = rst.begin() + cnt; it != rst.end(); ++it)
    {
        cout << it->first << " " << it->second << endl;
    }

    return 0;
}