I have studied the theory of the merge sort but don't have any idea of how to implement it in C++. My question is, merge sort creates arrays in recursion. But when implementing, how do we create arrays in runtime? or what is the general approach for this?
Thanks.
If the array has multiple elements, split the array into halves and recursively invoke the merge sort on each of the halves. Finally, when both halves are sorted, the merge operation is applied. Merge operation is the process of taking two smaller sorted arrays and combining them to eventually make a larger one.
Like QuickSort, Merge Sort is a Divide and Conquer algorithm. It divides the input array into two halves, calls itself for the two halves, and then it merges the two sorted halves. The merge() function is used for merging two halves.
To answer the question: Creating dynamically sized arrays at run-time is done using std::vector<T>
. Ideally, you'd get your input using one of these. If not, it is easy to convert them. For example, you could create two arrays like this:
template <typename T>
void merge_sort(std::vector<T>& array) {
if (1 < array.size()) {
std::vector<T> array1(array.begin(), array.begin() + array.size() / 2);
merge_sort(array1);
std::vector<T> array2(array.begin() + array.size() / 2, array.end());
merge_sort(array2);
merge(array, array1, array2);
}
}
However, allocating dynamic arrays is relatively slow and generally should be avoided when possible. For merge sort you can just sort subsequences of the original array and in-place merge them. It seems, std::inplace_merge()
asks for bidirectional iterators.
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