Well, I think this is a good exercise for anyone learning C.
Yes, as other buddies mentioned, you may go with the 'partition then partial sort' approach.
But since 'pointer of function' is a key function of C,
you will face it sooner or later,
now it is a good point to take a glimpse to it.
When 'sorting', it important to define 'which one is greater'.
Like
#include <stdio.h>
#include <string.h>
int normal_is_greater(int a, int b){
return a > b;
}
void plain_buble(int arr[], int n)
{ // as the name says, this is a 'plain buble sort'
int i,j;
for (i=0; i< n; i++) {
for (j = 0 ; j < (n-i-1); j++){
if ( normal_is_greater(arr[j], arr[j+1]) )
{
int temp = arr[j];
arr[j] = arr[j+1];
arr[j+1] = temp;
}
}
}
}
int special_is_greater(int a, int b){
if (a>=0 && b <0) {
return 0;
} else if ( a<0 && b >=0) {
return 1;
} else if ( a<0 && b <0) {
return a < b;
}
else
return a > b;
}
void buble_using_special_comparer(int arr[], int n)
{ // copy-pasted from 'plain_buble', but substitute a single row.
int i,j;
for (i=0; i< n; i++) {
for (j = 0 ; j < (n-i-1); j++){
if ( special_is_greater(arr[j], arr[j+1]) ) // <== yes, here
{
int temp = arr[j];
arr[j] = arr[j+1];
arr[j+1] = temp;
}
}
}
}
int main()
{
int arr[] = {1 ,-1 ,-3 , -2, 7, 5, 11, 6 };
int n = sizeof(arr)/sizeof(arr[0]);
plain_buble(arr, n);
for (int i = 0; i < n; i++)
{
printf("%d ", arr[i]);
}
printf("\n");
buble_using_special_comparer(arr, n);
for (int i = 0; i < n; i++)
{
printf("%d ", arr[i]);
}
printf("\n");
return 0;
}
Result:
-3 -2 -1 1 5 6 7 11
1 5 6 7 11 -1 -2 -3
As long as we have a 'plain_buble' sort function,
we can modify a bit to turn it into 'the sort we want'.
But the above sample is still not cool,
because plain_buble and buble_using_special_comparer are almost the same.
We can use 'pointer of function' to do the magic.
Like:
#include <stdio.h>
#include <string.h>
typedef int (* CompareFunc)(int a, int b);
void buble_sort(int arr[], int n, CompareFunc is_greater)
{ // as the name says, this is a 'plain buble sort'
int i,j;
for (i=0; i< n; i++) {
for (j = 0 ; j < (n-i-1); j++){
if (is_greater(arr[j], arr[j+1]) )
{
int temp = arr[j];
arr[j] = arr[j+1];
arr[j+1] = temp;
}
}
}
}
int normal_is_greater(int a, int b){
return a > b;
}
int special_is_greater(int a, int b){
if (a>=0 && b <0) {
return 0;
} else if ( a<0 && b >=0) {
return 1;
} else if ( a<0 && b <0) {
return a < b;
}
else
return a > b;
}
int main()
{
int arr[] = {1 ,-1 ,-3 , -2, 7, 5, 11, 6 };
int n = sizeof(arr)/sizeof(arr[0]);
buble_sort(arr, n, normal_is_greater);
for (int i = 0; i < n; i++)
{
printf("%d ", arr[i]);
}
printf("\n");
buble_sort(arr, n, special_is_greater);
for (int i = 0; i < n; i++)
{
printf("%d ", arr[i]);
}
printf("\n");
return 0;
}
