void Functions::topDownSplitMerge(RefArrayXd array1, RefArrayXd arrayCopy1, RefArrayXd array2, RefArrayXd arrayCopy2, int beginIndex, int endIndex)
{
// If input array1 contains only 1 element it is already sorted
if (endIndex - beginIndex < 2)
return;
// Find mid-point of the input array
int middleIndex = (endIndex + beginIndex) / 2;
// Separate first-half and second-half of the array and repeat the process
topDownSplitMerge(array1, arrayCopy1, array2, arrayCopy2, beginIndex, middleIndex);
topDownSplitMerge(array1, arrayCopy1, array2, arrayCopy2, middleIndex, endIndex);
// Order elements in each half and merge them into a single, sorted, array
topDownMerge(array1, arrayCopy1, array2, arrayCopy2, beginIndex, middleIndex, endIndex);
// Copy elements of array sorted into original array
int length = endIndex - beginIndex;
array1.segment(beginIndex, length) = arrayCopy1.segment(beginIndex, length);
array2.segment(beginIndex, length) = arrayCopy2.segment(beginIndex, length);
}
void CMergeSort::topDownSplitMerge(std::vector<double> * inputA, int iBegin, int iEnd, std::vector<double> * outputB)
{
int iMiddle; // for separating the array into two smaller array
if (iEnd - iBegin < 2) // the array has maximum 1 number
return;
iMiddle = (iEnd + iBegin) / 2;
topDownSplitMerge(inputA, iBegin, iMiddle, outputB); // left half
topDownSplitMerge(inputA, iMiddle, iEnd, outputB); // right half
topDownMerge(inputA, iBegin, iMiddle, iEnd, outputB); // merge two halves
copyArray(inputA, iBegin, iEnd, outputB);
}
void Functions::topDownMergeSort(RefArrayXd array1, RefArrayXd array2)
{
assert(array1.size() == array2.size());
ArrayXd arrayCopy1 = array1;
ArrayXd arrayCopy2 = array2;
topDownSplitMerge(array1, arrayCopy1, array2, arrayCopy2, 0, arrayCopy1.size());
}
std::vector<double> CMergeSort::run(std::vector<double> inputA)
{
std::vector<double>* outputB= new std::vector<double>(inputA);
topDownSplitMerge(&inputA, 0, inputA.size(), outputB);
return inputA;
}