[wplug] OT - programming logic help

[Chris Romano]

On Thu, Apr 23, 2009 at 11:39 AM, Ryan W. Frenz <rfrenz at gmail.com> wrote:
>> On Thu, Apr 23, 2009 at 10:58 AM, Chris Romano <romano.chris at gmail.com> wrote:
>>> Here are all the possible combos ... (it's easy to do on paper, just
>>> can't figure how to do this with code).
>
> Hi Chris,
>
> The below is in C++, but like you said, the logic should transfer to
> any language.  The key is the recursion.
>
> Ryan
>
> #include <iostream>
> #include <vector>
> #include <algorithm>
>
> typedef std::vector<int> NumberList;
> typedef std::vector<NumberList> ListPermutation;
>
> ListPermutation getPermutations(NumberList numbers) {
>        ListPermutation returns;
>
>        // Prune the recursion, just return both permutations of the pair.
>        if (numbers.size() == 2) {
>                returns.push_back(numbers);
>                std::swap(numbers[0], numbers[1]);
>                returns.push_back(numbers);
>                return returns;
>        }
>
>        int index = 0;
>        for (NumberList::const_iterator nIt = numbers.begin(); nIt !=
> numbers.end(); ++nIt, ++index) {
>                // Remove the current number and compute permutations of the others.
>                NumberList otherNumbers(numbers);
>                otherNumbers.erase(otherNumbers.begin() + index);
>
>                // Add the 'fixed' number to the sub-permutations.
>                const ListPermutation subPerm = getPermutations(otherNumbers);
>                for (ListPermutation::const_iterator lpIt = subPerm.begin(); lpIt !=
> subPerm.end(); ++lpIt) {
>                        NumberList fullPerm;    fullPerm.push_back(*nIt);
>                        fullPerm.insert(fullPerm.end(), (*lpIt).begin(), (*lpIt).end());
>                        returns.push_back(fullPerm);
>                }
>        }
>
>        return returns;
> }
>
> int main(int argc, char* argv[]) {
>        NumberList vals;
>        vals.push_back(1);
>        vals.push_back(2);
>        vals.push_back(3);
>        vals.push_back(4);
>        vals.push_back(5);
>
>        const ListPermutation perms = getPermutations(vals);
>        for (ListPermutation::const_iterator pIt = perms.begin(); pIt !=
> perms.end(); ++pIt) {
>                for (NumberList::const_iterator ppIt = (*pIt).begin(); ppIt !=
> (*pIt).end(); ++ppIt)
>                        std::cerr << *ppIt << " ";
>                std::cerr << "\n";
>        }
> }
>

It's been a while since I looked at C++ or really any OOP code but I
will start digging through that.  Thanks

And George ... thanks for the link.  I'm reading through that now


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