面试题：一千万条短信中，找到重复次数最多的10条

#include<iostream>
#include<fstream>
#include <string>
#include <unordered_map>
#include <vector>
#include <algorithm>
#include <queue>

using namespace std;

typedef unsigned long int uint64_t;

//获取字符串的hash值
uint64_t getHash(const string& s) {
    uint64_t hashVal = 0;
    uint64_t a = 3589;
    uint64_t b = 81369;
    for (char ch : s) {
        hashVal = hashVal * a + ch;
        a = a * b;
    }
    return hashVal;
}

struct posAndCount {
    int pos;
    int count;
    posAndCount(int a = 0, int b = 0) :
            pos(a), count(b) {
    };
};

struct NameHashPosAndCount {
    uint64_t namehash;
    int pos;
    int count;

    friend bool operator <(const NameHashPosAndCount& a,
            const NameHashPosAndCount& b) {
        return a.count > b.count;
    }
};


//从N个数据中找出出现次数最多的N个
void MfromN() {
    unordered_map<uint64_t, posAndCount> names;
    unordered_map<uint64_t, posAndCount>::iterator it;
    posAndCount pc;
    int pos = 0;

    ifstream fin("message.txt");
    string l;
    while (fin >> l) {
        uint64_t hashVal = getHash(l);
        it = names.find(hashVal);
        if (it == names.end()) {
            pc.pos = pos;
            pc.count = 0;
            names[hashVal] = pc;
        } else {
            names[hashVal].count++;
        }
        pos++;
    }
    fin.close();


    //优先队列寻找出现次数最多的10条
    priority_queue<NameHashPosAndCount> name10;
    NameHashPosAndCount n;
    for (it = names.begin(); it != names.end(); it++) {
        if (name10.size() < 10) {
            n.namehash = it->first;
            n.pos = it->second.pos;
            n.count = it->second.count;
            name10.push(n);
        } else {
            if (name10.top().count < it->second.count) {
                name10.pop();
                n.namehash = it->first;
                n.pos = it->second.pos;
                n.count = it->second.count;
                name10.push(n);
            }
        }
    }
    vector<int> index;
    while (!name10.empty()) {
        index.push_back(name10.top().pos);
        name10.pop();
    }
    sort(index.begin(),index.end());

    ifstream fin2("message.txt");
    int i = 0;
    int k = 0;
    while(k < 10 && fin2 >> l){
        if(i == index[k]){
            cout << l << endl;
            k++;
        }
        i++;
    }
    fin2.close();
}