Sort by Even and Odd numbers

Question

I would like to know is it possible to sort number by even or odd using the std::sort function.

I have the following codes but i am not sure how to implement in the

Answer 1

The catch is that there are two functions you can use.

template< class BidirectionalIterator, class UnaryPredicate >
BidirectionalIterator partition( BidirectionalIterator first, BidirectionalIterator last, UnaryPredicate p );

template< class BidirectionalIterator, class UnaryPredicate >
BidirectionalIterator stable_partition( BidirectionalIterator first, BidirectionalIterator last, UnaryPredicate p );

The functions partition() and stable_partition() reorganize elements of the collection in such a way that all elements for which predicate p returns true will precede all those for which p returns false. It means that the elements will be divided into two ranges:

• [first, return_value)

• [return_value, last)

where return_value is the iterator returned by either of functions. The sequence of elements in the resulting groups is where partition() and stable_partition() differ.

partition() does not guarantee any particular order within the ranges.

stable_partition() will keep a relative order of elements before the split. It means that if there are two elements a and b, and a precedes b, and if they both belong to the same group after the split, element a will still precede element b.

Here is a sample code:

#include 
#include 
#include 
using namespace std;

bool IsOdd(int i) {
    return (i & 1); //use !(i & 1); if you want to place even elements first in the vector
}

int main() {
    vector v;
    // set some values and shuffle them:
    for (int i = 1; i<10; ++i)
        v.push_back(i);
    random_shuffle(v.begin(), v.end());

    cout << "All elements:";
    for (vector::iterator it = v.begin(); it != v.end(); ++it)
        cout << ' ' << *it;
    cout << endl;

    //sort the vector
    cout << "Sorted vector:";
    sort(v.begin(), v.end());
    for (vector::iterator it = v.begin(); it != v.end(); ++it)
        cout << ' ' << *it;
    cout << endl;

    //change to partition and see the difference
    vector::iterator bound = stable_partition(v.begin(), v.end(), IsOdd);

    // print content:
    cout << "odd elements:";
    for (std::vector::iterator it = v.begin(); it != bound; ++it)
        cout << ' ' << *it;
    cout << endl;

    cout << "even elements:";
    for (vector::iterator it = bound; it != v.end(); ++it)
        cout << ' ' << *it;
    cout << endl;

    cout << "Sorted odd-even vector:";
    for (vector::iterator it = v.begin(); it != v.end(); ++it)
        cout << ' ' << *it;
    cout << endl;

    return 0;
}

Output:

All elements: 5 6 2 1 9 4 7 8 3
Sorted vector: 1 2 3 4 5 6 7 8 9
odd elements: 1 3 5 7 9
even elements: 2 4 6 8
Sorted odd-even vector: 1 3 5 7 9 2 4 6 8

I hope it helps for understanding.