Permutation Help?

[whoovian11]

So i know how to do permutation when you have numbers listed as 1,2,3,4 but how do u write a program where the input file is just "15 , 10"and you have to make 10 permutations for 1-15? I have to do it using a source set

[jumper007]

All you have to do is generate an array with the numbers in the range 1-15, then pass that array to the backtracking function which does the permutations. In the backtracking algorithm, simply add a counter and when it reaches 10, use return/break (depending on your implementation recursive/iterative).

Raul

[whoovian11]

can i plz get like a pseudocode ?

[jumper007]

Well, you can put here the pseudocode for the 1,2,3,4 permutation (as you mentioned, you know how to do that), and I'll just tell you where to make changes. Actually, if I had more time right now, I would write it myself, but I'm a little busy, sorry for that.

Raul

[LB]

There are numerous tutorials on the internet, including one on this site, explaining how to use files in C++. As long as you don't use .open(), .close(), or .eof(), you should be fine with any tutorial.

[whoovian11]

I am confused because i have use 2 vectors and regenerate random permutation

[giblit]

If you are using vectors can you use the built in std::next_permutation or do you have to use your own? Either way just get the next permutation 10 times and you are good to go.

[whoovian11]

i have to use my own?? Help

[giblit]

Is that a question or a statement?

[whoovian11]

statement sorry..
So i have use my own.
Make 15 random permutation (vector)
and 10 is the highest number in each permutation (vector)

[giblit]

Can you not call your permutation function 10 times with the 15 random numbers?

[whoovian11]

how do u do that ?

[giblit]

Okay do you have to make your permutation function or do you have it done already? Also, if you could post what you have so far it would be helpful.

[whoovian11]

i am not sure if i am doing this right
void permutaion(const vector<int> &now,
vector<int> &next)
{
int size=now.size();
if(size>0)
{
for(int cnt=0; cnt<size;++cnt)
{
vector<int> vt;

vector<int>::const_iterator it=now.begin();
for(int cnt1=0;cnt1<size;++cnt1)
{
if(cnt1==cnt)
{
++it;
continue;
}
else
.push_back(*it);
++it;

[giblit]

Honestly I am not sure what you are doing(or trying) in your code. It looks a bit odd.

If the upper limit is 15 instead of 10 then so you could have something like:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 2 3 4 5 6 7 8 9 10 11 12 13 15 14
1 2 3 4 5 6 7 8 9 10 11 12 14 13 15
1 2 3 4 5 6 7 8 9 10 11 12 14 15 13
1 2 3 4 5 6 7 8 9 10 11 12 15 13 14
1 2 3 4 5 6 7 8 9 10 11 12 15 14 13

...

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

These links may help you:
http://stackoverflow.com/questions/11483060/stdnext-permutation-implementation-explanation
http://www.cplusplus.com/reference/algorithm/next_permutation/
http://en.cppreference.com/w/cpp/algorithm/next_permutation

Here is a basic implemenation on cppreference

template<class BidirIt>
bool next_permutation(BidirIt first, BidirIt last)
{
    if (first == last) return false;
    BidirIt i = last;
    if (first == --i) return false;
 
    while (1) {
        BidirIt i1, i2;
 
        i1 = i;
        if (*--i < *i1) {
            i2 = last;
            while (!(*i < *--i2))
                ;
            std::iter_swap(i, i2);
            std::reverse(i1, last);
            return true;
        }
        if (i == first) {
            std::reverse(first, last);
            return false;
        }
    }
}

You can possibly fix your code by learning from this.