读取文件并找出年龄最大的N个人-兰亭集市笔试题

C++ code:

#include <iostream>
#include <fstream>
#include <map>
#include <string>
#include <algorithm>

using namespace std;

int main()
{
    multimap<int,string> agemap;//以年龄为键，以个人信息为值，年龄必有重复，定义成multimap可自动排序
    ifstream infile("persons.txt");//为ifstream对象提供文件名作为初始化式，就相当于打开了特定的文件，不用再调用open函数
    if(!infile)
    {
        cout<<"Open file error!"<<endl;
    }

    string textline;
    int age;
    string::reverse_iterator rcomma;//string类型反向迭代器，用于指向反向搜索找到的第一个逗号
    while(getline(infile,textline))//getline函数将istream参数作为返回值，可用作读取结束判断条件
    {
        rcomma=find(textline.rbegin(),textline.rend(),',');//rcomma指向从后往前的最后一个逗号
        age=atoi(string(rcomma.base(),textline.end()).c_str());//string转int，rcomma.base()表示将反向迭代器rcomma转换为从前往后移动的普通迭代器
        agemap.insert(make_pair(age,textline));//将年龄和完整信息插入multimap
    }

    multimap<int,string>::reverse_iterator map_it=agemap.rbegin();//从后往前输出

    int N=10;//假定要输出年龄最大的前10个
    while(map_it!=agemap.rend() && N-- >0)//按年龄降序输出元素
    {
        cout<<map_it->second<<endl;
        ++map_it;
    }

    return 0;
}

 

persons.txt

Ted Elliott,9876541198611121512,27
Peter Twist,52478198901243122,24
Terry Rossio,456871198804096012,25
George Marshall Ruge,510402198904070919,24
Brian Morris,51068119830104411X,30
Christopher Masterson,432502198908193032,24
Mel Colm-Cille Gerard Gibson,431102198911046233,24
Tim,511621198603095910,27
gdfgdf,371326198806230018,25
gdfg,41150219871015966X,26
gdfdf,620422198801191911,25
gdfgfd,411325198710241333,26
gdff,140522198804301013,25
gdfg,230204198801180714,25
dfgfd,510704198706063514,26
gfdgdf,610424198906172881,24
gdfgfd,513922198511210031,28
uykuy,320911198901061214,24
jghjj,51302919890906659X,24
jhhjh,612731198809280436,25
jhgjhg,650103198902056022,24
jghg,51070319790525972X,34
jghjh,510681198810130315,25
hgjhg,510304198706071010,26
jghjhg,320382198708300431,26
jhgjg,340321198903154709,24