Debug of a very simple recursion problem

Question

Meowooo 2017-10-21

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https://ww2.mathworks.cn/matlabcentral/answers/362444-debug-of-a-very-simple-recursion-problem

评论： Walter Roberson 2017-10-21

在 MATLAB Online 中打开

The idea of the problem is to reverse a character array using recursion.

1. Write a function called charReversal with the following function signature:

1 f u n c ti o n a r r a y 2 = c h a r R e v e r s al ( a r r a y 1 )

where array1 is the input character array, and array2 is the reversal of array1. For example, charReversal(’abcde’) should return ’edcba’.

My answer:

function array2 = charReversal(array1)
    %arrary1 is the input character array
    %arrary2 is the reversal of array1
    if numel(array1)<2
       array2 = array1;
    else 
       array2 = reverse(array1);
end

Question: I don't know where to to put the base case, what the base case should be.

Thank you very much.

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Answer 1

Walter Roberson 2017-10-21

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https://ww2.mathworks.cn/matlabcentral/answers/362444-debug-of-a-very-simple-recursion-problem#answer_286951

在 MATLAB Online 中打开

    if numel(array1)<2
       array2 = array1;

is already handling the base case. But the rest of your code needs to be developed to use recursion.

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Meowooo 2017-10-21

How could I add the recursion then? I thought it was in recursion already.

Walter Roberson 2017-10-21

The function does not call itself, and does not call any function that calls the function, so No, it is not already recursive.

Hint:

What happens if you remove one character and reverse the rest, and then somehow combine the one removed character with what was returned from reversing the rest?

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