PAT/PATAdvanced/1028.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

typedef struct {
	int ID;
	char name[9];
	int grade;
} Student, *pStudent;

/* increasing by ID */
int cmp1(const void *a, const void *b)
{
	pStudent s1 = *(pStudent*)a, s2 = *(pStudent*)b;
	return s1->ID - s2->ID;
}

/* non decreasing by name, then increasing by ID */
int cmp2(const void *a, const void *b)
{
	pStudent s1 = *(pStudent*)a, s2 = *(pStudent*)b;
	if (strcmp(s1->name, s2->name))
		return strcmp(s1->name, s2->name);
	else
		return s1->ID - s2->ID;
}

/* non decreasing by grade, then increasing by ID */
int cmp3(const void *a, const void *b)
{
	pStudent s1 = *(pStudent*)a, s2 = *(pStudent*)b;
	if (s1->grade - s2->grade)
		return s1->grade - s2->grade;
	else
		return s1->ID - s2->ID;
}

int main()
{
	int N, C;
	Student buffer[100000] = {0};
	pStudent students[100000] = {0}, *s = students;

	scanf("%d %d", &N, &C);
	for (int i = 0; i < N; i++, s++) {
		/* use a new struct buffer */
		*s = buffer + i;
		scanf("%d %s %d", &(*s)->ID, (*s)->name, &(*s)->grade);
	}

	if (C == 1)  /* increasing ID */
		qsort(students, N, sizeof(pStudent), cmp1);
	else if (C == 2)  /* non-decreasing name */
		qsort(students, N, sizeof(pStudent), cmp2);
	else  /* C == 3, non-decreasing grade */
		qsort(students, N, sizeof(pStudent), cmp3);

	for (int i = 0; i < N; i++)
		printf("%06d %s %d\n", students[i]->ID,
							   students[i]->name,
							   students[i]->grade);

	return 0;
}