Why doesn't recursion in my mergeSort algorithm work?

Question

Jethro Djan 2022-10-7

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https://ww2.mathworks.cn/matlabcentral/answers/1819250-why-doesn-t-recursion-in-my-mergesort-algorithm-work

编辑： Jethro Djan 2022-10-7

I am following a book on algorithms and want to implement mergeSort myself. The problem is that I cannot get the desired ordering of my input array Arr. Have debugged and seen the problem but can't find a solution [which is that anything after mergeSort(Arr, p, q) is not executed at all]. In other languages like C, this would execute fine. Is there something missing [with respect to MATLAB] that will get the recursion to work?

function [sortedA] = mergeSort(Arr, p, r)
if p < r
    q = floor((p + r)/2);
    mergeSort(Arr, p, q);
    mergeSort(Arr, q + 1, r);
    merge(Arr, p, q, r);
end
sortedA = Arr;
end

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Answer 1

Jethro Djan 2022-10-7

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1819250-why-doesn-t-recursion-in-my-mergesort-algorithm-work#answer_1068680

编辑：Jethro Djan 2022-10-7

在 MATLAB Online 中打开

Apparently I didn't realise the fundamental error in my assumption which is that when dealing with arrays (or vectors in the case of MATLAB), I don't have default access to manipulating the pointers as would be in C. I have to deal with arrays by copying them around.

Edit: In case anyone is wondering what I ended up doing, it was something like this:

function [sortedA] = mergeSort(Arr, p, r)
if p < r
    q = floor((p + r)/2);
    leftArr = mergeSort(Arr(p:q));
    rightArr = mergeSort(Arr(q+1:r));
    sortedA = merge(leftArr, rightArr);
end
end