# Sort an array a[0...n-1].
gaps = [701, 301, 132, 57, 23, 10, 4, 1]
foreach (gap in gaps)
# Do an insertion sort for each gap size.
for (i = gap; i < n; i += 1)
temp = a[i]
for (j = i; j >= gap and a[j - gap] > temp; j -= gap)
a[j] = a[j - gap]
a[j] = temp
this is the pseudocode in Wikipedia page. I'm not sure about that if my c++ code is correct according to it. Here is my code:
void shellSort(int *array, int array_size)
{
int e, i, j, temp;
for(e = 0; e < array_size; e++)
{
for( i = e; i < array_size; i++)
{
temp = array[i];
for( j = i; j >= e && array[j - e] > temp; j -= e)
{
array[j] = array[j-e];
}
array[j] = array[temp];
}
}
}
And here is my test code:
int main()
{
int sizes[9] = {9,3,5,7,1,0,6,2,4};
int size = 0;
shellSort(sizes,size);
for(int i=0;i<size;i++)
{
cout << sizes[i] << endl;
}
return 0;
}
but it shows nothing on the screen.
Okay, let's take this from the top
void shellSort(int *array, int array_size)
{
Your code completely omitted the needed gaps array
const int gaps[] = {701, 301, 132, 57, 23, 10, 4, 1};
int e, i, j, temp;
The outer loop needs to be across gaps rather than 0 to array_size
for(e = 0; e < sizeof(gaps)/sizeof(int); ++e)
{
int gap = gaps[e];
You need to use the gap from the gaps array in the inner loop
for( i = gap; i < array_size; ++i)
{
temp = array[i];
for( j = i; j >= gap && array[j - gap] > temp; j -= gap)
{
array[j] = array[j-gap];
}
You need to store temp back into the array
array[j] = temp;
}
}
}
NB: I don't have a compiler to hand right now, so I haven't checked that, but I think it's right.
Also, a few minor points, this:
int e, i, j, temp;
is bad practice, instead declare each variable as you use it, i.e. do this instead:
for( int i = gap; i < array_size; ++i)
{
int temp = array[i];