PAT甲级(Advanced Level)练习题 List Sorting (25)

题目描述

Excel can sort records according to any column. Now you are supposed to imitate this function.

输入描述:

Each input file contains one test case. For each case, the first line contains two integers N (<=100000) and C, where N is the number of records and C is the column that you are supposed to sort the records with. Then N lines follow, each contains a record of a student. A student’s record consists of his or her distinct ID (a 6-digit number), name (a string with no more than 8 characters without space), and grade (an integer between 0 and 100, inclusive).

输出描述:

For each test case, output the sorting result in N lines. That is, if C = 1 then the records must be sorted in increasing order according to ID’s; if C = 2 then the records must be sorted in non-decreasing order according to names; and if C = 3 then the records must be sorted in non-decreasing order according to grades. If there are several students who have the same name or grade, they must be sorted according to their ID’s in increasing order.

输入例子:

3 1
000007 James 85
000010 Amy 90
000001 Zoe 60

输出例子:

000001 Zoe 60
000007 James 85
000010 Amy 90

题目分析及实现方法

原本的想法是自己根据所给的列实现排序，用了选择排序的方法，但是其算法复杂度较高，导致三个用例运行超时，查询资料后发现可以调用"#include《algorithm》"中的sort函数，只需要自己写好比较函数即可快速的排序。下次遇到排序的题，首先要想到sort函数，而不是自己去实现排序算法。

代码实现（选择排序超时版本）

#include <iostream>
#include <algorithm>
using namespace std;

struct Student{
    string id;
    string name;
    int grade;
};


int main()
{
    int num ,col;
    cin >>num >>col;
    Student stu[num];
    for(int i = 0; i<num ; i++){
        string id,name;
        int grade;
        cin >> stu[i].id >> stu[i].name>>stu[i].grade;
    }

    if(col == 1){
        for(int i =0; i< num;i++){
        string min = stu[i].id;
        int temp = 0;
        for(int j =i+1;j<num;j++){
            if(stu[j].id < min){
                min = stu[j].id;
                temp = j;
            }
        }
        if(i<temp)
        swap(stu[i],stu[temp]);
        }
    }else if(col ==2){
        for(int i =0; i< num;i++){
            string min = stu[i].name;
            string minID = stu[i].id;
            int temp = 0;
            for(int j =i+1;j<num;j++){
                if(stu[j].name <= min){
                    if(stu[j].name == min){
                        if(stu[j].id < minID){
                             minID = stu[j].id;
                             min = stu[j].name;
                             temp = j;
                        }
                    }else{
                            minID = stu[j].id;
                            min = stu[j].name;
                            temp = j;
                    }
                }
            }
            if(i<temp)
                swap(stu[i],stu[temp]);
        }
    }else if(col == 3){
        for(int i =0; i< num;i++){
            int min = stu[i].grade;
            string minID = stu[i].id;
            int temp = 0;
            for(int j =i+1;j<num;j++){
                if(stu[j].grade <= min){
                    if(stu[j].grade == min){
                        if(stu[j].id < minID){
                             minID = stu[j].id;
                             min = stu[j].grade;
                             temp = j;
                        }
                    }else{
                            minID = stu[j].id;
                            min = stu[j].grade;
                            temp = j;
                    }
                }
            }
            if(i<temp)
                swap(stu[i],stu[temp]);
        }
    }
    for(int i =0 ;i<num;i++){
        cout<<stu[i].id<<" "<<stu[i].name<<" "<<stu[i].grade<<endl;
    }

    return 0;
}

正确解法（C++实现版本）

#include <iostream>
#include <algorithm>

using namespace std;
int num ,col;
struct Student{
    string id;
    string name;
    int grade;
};

bool cmp1(Student a,Student b) {
    if(col==1)
        return a.id < b.id;
    else if(col==2){
      if(a.name == b.name)
        return a.id < b.id;
      else
        return a.name<b.name;
    }
    else{
      if(a.grade==b.grade)
        return a.id<b.id;
      else
        return a.grade<b.grade;
    }
}


int main()
{

    cin >>num >>col;
    Student stu[num];
    for(int i = 0; i<num ; i++){
        string id,name;
        int grade;
        cin >> stu[i].id >> stu[i].name>>stu[i].grade;
    }

    sort(stu,stu+num,cmp1);
    for(int i =0 ;i<num;i++){
        cout<<stu[i].id<<" "<<stu[i].name<<" "<<stu[i].grade<<endl;
    }

    return 0;
}