int RandomizedSelect(std::vector<int> & nums, int start, int end, int i)
{
if (nums.empty()) return 0;
if (start == end) return nums[start];
int mid = RandomizedPartition(nums, start, end);
int k = mid - start + 1;
if (i == k)
return nums[mid];
else if (i < k)
return RandomizedSelect(nums, start, mid - 1, i);
else
return RandomizedSelect(nums, mid + 1, end, i - k);
}
int main()
{
int64_t array[] = { 2, 8, 7, 1, 3, 5, 6, 4 };
std::cout << RandomizedSelect(array, 0, 7, 3) << std::endl;
getchar();
return 0;
}
// -----------------------------------------------------------------------------
// Sort the entries of filtMagUpdateMap and set the threshold to be ? percentile
// -----------------------------------------------------------------------------
Real_t BFReconstructionEngine::SetNonHomThreshold(RealImageType::Pointer magUpdateMap)
{
size_t dims[1] =
{ m_Geometry->N_z* m_Geometry->N_x};
RealArrayType::Pointer TempMagMap = RealArrayType::New(dims, "TempMagMap");
uint32_t ArrLength = m_Geometry->N_z * m_Geometry->N_x;
Real_t threshold;
//Copy into a new list for sorting
Real_t* src = magUpdateMap->getPointer();
Real_t* dest = TempMagMap->getPointer();
::memcpy(dest, src, ArrLength * sizeof(Real_t));
#ifdef DEBUG
Real_t TempSum = 0;
for(uint32_t i = 0; i < ArrLength; i++)
{ TempSum += TempMagMap->d[i]; }
if(getVerbose()) { std::cout << "Temp mag map average= " << TempSum / ArrLength << std::endl; }
#endif //DEBUG
/* for (uint32_t i = 0; i < m_Geometry->N_z; i++)
for (uint32_t j = 0; j < m_Geometry->N_x; j++)
{
//TempMagMap->d[i*geometry->N_x+j]=i*geometry->N_x+j;
TempMagMap->d[i * (uint32_t)m_Geometry->N_x + j] = magUpdateMap->getValue(i, j);
} */
uint32_t percentile_index = ArrLength / MBIR::Constants::k_NumNonHomogeniousIter;
if(getVerbose()) { std::cout << "Percentile to select= " << percentile_index << std::endl; }
//Partial selection sort
/*Real_t max;
uint32_t max_index;
for (uint32_t i = 0; i <= percentile_index; i++)
{
max = TempMagMap->d[i];
max_index = i;
for (uint32_t j = i + 1; j < ArrLength; j++)
{
if(TempMagMap->d[j] > max)
{
max = TempMagMap->d[j];
max_index = j;
}
}
Real_t temp = TempMagMap->d[i];
TempMagMap->d[i] = TempMagMap->d[max_index];
TempMagMap->d[max_index] = temp;
}
threshold = TempMagMap->d[percentile_index];*/
threshold = RandomizedSelect(TempMagMap, 0, ArrLength - 1, ArrLength - percentile_index);
return threshold;
}
int64_t RandomizedSelect(int64_t* A, int64_t p, int64_t r, int64_t i)
{
if (p == r)
{
return A[p];
}
int64_t q = RandomizedPartition(A, p, r);
int64_t k = q - p + 1;
if (i == k)
{
return A[q];
}
else if (i < k)
{
return RandomizedSelect(A, p, q - 1, i);
}
else
{
return RandomizedSelect(A, q + 1, r, i - k);
}
}
int Find::RandomizedSelect(int a[], int p, int r, int pos)
{
//if p == r, the pos = 1
if (p == r)
{
return a[p];
}
int q = Common::RandParition(a, p, r);
//min array size
int k = q - p + 1;
if (pos == k)
{
return a[q];
}
else if (pos < k)
{
return RandomizedSelect(a, p, q - 1, pos);
}
else
{
return RandomizedSelect(a, q + 1, r, pos - k);
}
}
