Excel can sort records according to any column. Now you are supposed to imitate this function.
Input
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).
Output
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.
Sample Input 1
3 1
000007 James 85
000010 Amy 90
000001 Zoe 60
Sample Output 1
000001 Zoe 60
000007 James 85
000010 Amy 90
Sample Input 2
4 2
000007 James 85
000010 Amy 90
000001 Zoe 60
000002 James 98
Sample Output 2
000010 Amy 90
000002 James 98
000007 James 85
000001 Zoe 60
Sample Input 3
4 3
000007 James 85
000010 Amy 90
000001 Zoe 60
000002 James 90
Sample Output 3
000001 Zoe 60
000007 James 85
000002 James 90
000010 Amy 90

题意：
首先输入两个数N和c，N是接下来输入的数据条数，c是排序方式。
c=1用ID升序；c=2用姓名升序；c=3用成绩升序。
若姓名或成绩相同，用ID升序排列（ID唯一）。

用的是结构体数组处理，然后用sort()排序，单独写3种排序方式按需调用即可。

注意：输入输出能用scanf/printf就别用cin/cout，会超时。

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

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

bool sortById(const student& a, const student& b){
    return a.id < b.id;
}

bool sortByName(const student& a, const student& b){
    if (a.name == b.name){
        return a.id < b.id;
    }
    else{
        return a.name < b.name;
    }
}

bool sortByGrade(const student& a, const student& b){
    if (a.grade == b.grade){
        return a.id < b.id;
    }
    else{
        return a.grade < b.grade;
    }
}

int main(){
    int n, c;
    scanf("%d %d", &n, &c);
    vector<struct student> v(n);
    for (int i = 0; i < n; ++i){
        scanf("%d", &v[i].id);
        cin >> v[i].name;
        scanf("%d", &v[i].grade);
    }
    if (1 == c){
        sort(v.begin(), v.end(), sortById);
    }
    else if (2 == c){
        sort(v.begin(), v.end(), sortByName);
    }
    else if (3 == c){
        sort(v.begin(), v.end(), sortByGrade);
    }
    for (int i = 0; i < n; ++i){
        printf("%06d ", v[i].id);
        cout << v[i].name;
        printf(" %dn", v[i].grade);
    }
    return 0;
}