private static int NumberOfShortestCombinations(int[] list, int initialGoal)
{
var memo = new SimpleMemo <ulong>();
var lengths = new SafeDictionary <int, int>();
Explore(list.Length, 0, initialGoal);
var shortestCombinations = lengths.OrderBy(x => x.Key).First().Value;
return(shortestCombinations);
void Explore(int size, uint pickmask, int goal)
{
if (goal == 0)
{
var len = pickmask.NumberOfSetBits();
lengths[len]++;
return;
}
if (goal < 0 || size == 0)
{
return;
}
if (memo.IsSeenBefore((ulong)size << 32 | pickmask))
{
return;
}
// For skipped item, pass 0 into the bit-mask (ie do nothing); for used item pass 1.
Explore(size - 1, pickmask << 1, goal);
Explore(size - 1, (pickmask << 1) + 1, goal - list[size - 1]);
}
}