I'm testing the speed of some functions so I made a test to run the functions over and over again and I stored the results in an array. I needed them to be sorted by the size of the array I randomly generated. I generate 100 elements. Merge sort to the rescue! I used this link to get me started.
The section of code I'm focusing on:
private void mergesort(int low, int high) {
// check if low is smaller then high, if not then the array is sorted
if (low < high) {
// Get the index of the element which is in the middle
int middle = low + (high - low) / 2;
// Sort the left side of the array
mergesort(low, middle);
// Sort the right side of the array
mergesort(middle + 1, high);
// Combine them both
merge(low, middle, high);
}
}
which translated to VB.NET is
private sub mergesort(low as integer, high as integer)
' check if low is smaller then high, if not then the array is sorted
if (low < high)
' Get the index of the element which is in the middle
dim middle as integer = low + (high - low) / 2
' Sort the left side of the array
mergesort(low, middle)
' Sort the right side of the array
mergesort(middle + 1, high)
' Combine them both
merge(low, middle, high)
end if
end sub
Of more importance the LOC that only matters to this question is
dim middle as integer = low + (high - low) / 2
In case you wanna see how merge sort is gonna run this baby
high low high low
100 0 10 0
50 0 6 4
25 0 5 4
12 0 12 7
6 0 10 7
3 0 8 7
2 0 :stackoverflow error:
The error comes from the fact 7 + (8 - 7) / 2 = 8. You'll see 7 and 8 get passed in to mergesort(low, middle) and then we infinite loop. Now earlier in the sort you see a comparison like this again. At 5 and 4. 4 + (5 - 4) / 2 = 4. So essentially for 5 and 4 it becomes 4 + (1) / 2 = 4.5 = 4. For 8 and 7 though it's 7 + (1) / 2 = 7.5 = 8. Remember the numbers are typecasted to an int.
Maybe I'm just using a bad implementation of it or my typecasting is wrong, but my question is: Shouldn't this be a red flag signaling something isn't right with the rounding that's occuring?
Without understanding the whole algorithm, note that VB.NET / is different than C# /. The latter has integer division by default, if you want to truncate decimal places also in VB.NET you have to use \.
Read: \ Operator
So i think that this is what you want:
Dim middle as Int32 = low + (high - low) \ 2