trying to understand permutation generation

Question

I am trying to understand a permutation algorithm given here what I am not clear is with first block of pseudo code where they mention

array = [1, 2, 3, 4]
function permutation(start, end):
#i will go from start to end
    for i -> (start, end+1):
        permutation(start+1,end)

why has end+1 used in for i loop this is not clear to me as far as I understand end+1 should go out of index of array to which permutation has to be applied, but this is not the case here this is what I am not clear with.

Answer 1

The author is familiar in Python, and uses the same (unfortunate) idiom in the pseudo code. In Python, the start of a range is inclusive, while the end is exclusive. Later on that page the Python code excerpt proves that that indeed is the case:

for i in range(start, end+1):

With this code i will be sequentially assigned all integers from start to end inclusive, but excluding the end + 1.

In C one would often use < in loops - then it would happen there too:

for (size_t i = start; start < end + 1; start++)
                               ^^^^^^^

though more natural would be to write

for (size_t i = start; start <= end; start++)