Use a bitmap(or hashmap), and recursively to get the permutation

permutate-recur.cpp

#include <iostream>

using namespace std;

// permutate recusively - use a bitmap, index as the permutate value.
// If the target to permutation value doesn't fit in a bitmap, just use a hashmap.
void permutate()
{
        static int a[] = {0, 0, 0, 0};
        static int o[4];
        static int oi = -1;
        for(int i = 0; i < sizeof(a)/sizeof(a[0]); ++i)
        {
                if(a[i] == 0)
                {
                        a[i] = 1;
                        oi++;
                        o[oi] = i + 1;
                        permutate();
                        oi--;
                        a[i] = 0;
                }
        }
        if(oi == 3)
        {
                for(int i = 0; i < 4; i++)
                        cout << o[i] << " ";
                cout << endl;
        }
}

int main()
{
        permutate();
}