1028 List Sorting

1028 List Sorting (25分)

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

Input Specification:

Each input file contains one test case. For each case, the first line contains two integers N (≤105) 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 Specification:

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

审题

本题按要求将结构体数组排序：

1. c==1,将数组按“id”字段递增排序

2. c==2,将数组按"name"字段非递减排序

3. c==3，将数组按“grade”按非递减排序

输出排序后的结果。

思路

排序题可用sort函数解决。不过要注意cmp函数的实现要注意：

sort函数的cmp必须按照规定来写，即必须只是 > 或者 <

比如: return a > b; return a < b;

而不能是 <= 或者 >= ，（实际上等于号加了也是毫无意义，sort是不稳定的排序），否则可能会出现段错误

坑点

本题输入输出用cin和cout会超时，改用scanf和printf可通过。使用printf和scanf的时候要注意不能直接输入输出string类型，要先分配空间。这里为了方便我直接用了字符数组，没有使用string。

参考代码

#include<iostream>
#include<cstdio>
#include<string.h>
#include<algorithm>
using namespace std;
​
typedef struct{
    char id[7];
    char name[10];
    int grade;
}stu;
​
bool cmp1(stu a,stu b){
    return strcmp(a.id,b.id)<0;
}
​
bool cmp2(stu a,stu b){
    if(strcmp(a.name,b.name)!=0){
        return strcmp(a.name,b.name)<0; 
    } else {
        return a.id<b.id;
    }
}
​
bool cmp3(stu a,stu b){
    if(a.grade!=b.grade){
        return a.grade<b.grade; 
    } else {
        return a.id<b.id;
    }
}
​
stu s[100001];
​
int main()
{
    int n,c;
    cin>>n>>c; 
    for(int i=0;i<n;i++){
        scanf("%s %s %d",&s[i].id,&s[i].name,&s[i].grade);
    }
    switch(c){
        case 1:
            sort(s,s+n,cmp1);
            break;
        case 2:
            sort(s,s+n,cmp2);
            break;
        case 3:
            sort(s,s+n,cmp3);
            break;
    }
    for(int i=0;i<n;i++){
        printf("%s %s %d\n",s[i].id,s[i].name,s[i].grade);
    }
}