Problem 52462. Easy Sequences 1: Find the index of an element

Created by Ramon Villamangca

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{"parts":[{"partUri":"/matlab/document.xml","contentType":"application/vnd.mathworks.matlab.code.document+xml","content":"<?xml version=\"1.0\" encoding=\"UTF-8\"?><w:document xmlns:w=\"http://schemas.openxmlformats.org/wordprocessingml/2006/main\"><w:body><w:p><w:pPr><w:pStyle w:val=\"text\"/><w:jc w:val=\"left\"/></w:pPr><w:r><w:t>The nth element of a series </w:t></w:r><w:customXml w:element=\"equation\"><w:customXmlPr><w:attr w:name=\"displayStyle\" w:val=\"false\"/></w:customXmlPr><w:r><w:t>A</w:t></w:r></w:customXml><w:r><w:t> is defined by: </w:t></w:r><w:customXml w:element=\"equation\"><w:customXmlPr><w:attr w:name=\"displayStyle\" w:val=\"false\"/></w:customXmlPr><w:r><w:t>A(n) = \\displaystyle\\sum\\limits_{k=1}^n (k\\cdot(-1)^{k^3+1})</w:t></w:r></w:customXml><w:r><w:t>. Obviously, the first element </w:t></w:r><w:customXml w:element=\"equation\"><w:customXmlPr><w:attr w:name=\"displayStyle\" w:val=\"false\"/></w:customXmlPr><w:r><w:t>A(1) = 1</w:t></w:r></w:customXml><w:r><w:t>. Given the nth element </w:t></w:r><w:customXml w:element=\"equation\"><w:customXmlPr><w:attr w:name=\"displayStyle\" w:val=\"false\"/></w:customXmlPr><w:r><w:t>A(n)</w:t></w:r></w:customXml><w:r><w:t>, find the value of the corresponding index </w:t></w:r><w:customXml w:element=\"equation\"><w:customXmlPr><w:attr w:name=\"displayStyle\" w:val=\"false\"/></w:customXmlPr><w:r><w:t>n</w:t></w:r></w:customXml><w:r><w:t>.</w:t></w:r></w:p></w:body></w:document>","relationship":null}],"relationships":[{"relationshipType":"http://schemas.mathworks.com/matlab/code/2013/relationships/document","target":"/matlab/document.xml","relationshipId":"rId1"}]}

<div style = "text-align: start; line-height: 20.4333px; min-height: 0px; white-space: normal; color: rgb(0, 0, 0); font-family: Menlo, Monaco, Consolas, monospace; font-style: normal; font-size: 14px; font-weight: 400; text-decoration: rgb(0, 0, 0); white-space: normal; "><div style="block-size: 66px; display: block; min-width: 0px; padding-block-start: 0px; padding-top: 0px; perspective-origin: 407px 33px; transform-origin: 407px 33px; vertical-align: baseline; "><div style="font-family: Helvetica, Arial, sans-serif; line-height: 21px; margin-block-end: 9px; margin-block-start: 2px; margin-bottom: 9px; margin-inline-end: 10px; margin-inline-start: 4px; margin-left: 4px; margin-right: 10px; margin-top: 2px; perspective-origin: 384px 33px; text-align: left; transform-origin: 384px 33px; white-space: pre-wrap; margin-left: 4px; margin-top: 2px; margin-bottom: 9px; margin-right: 10px; "><span style="block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 88.5px 8px; transform-origin: 88.5px 8px; unicode-bidi: normal; "><span style="">The nth element of a series </span></span><span style="font-family: &quot;STIXGeneral&quot;, &quot;STIXGeneral-webfont&quot;, serif; font-style: italic; font-weight: 400; color: rgb(0, 0, 0);">A</span><span style="block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 46px 8px; transform-origin: 46px 8px; unicode-bidi: normal; "><span style=""> is defined by: </span></span><span style="vertical-align:-17px"><img src="data:image/png;base64,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" style="width: 155.5px; height: 45px;" width="155.5" height="45"></span><span style="block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 91px 8px; transform-origin: 91px 8px; unicode-bidi: normal; "><span style="">. Obviously, the first element </span></span><span style="vertical-align:-5px"><img src="data:image/png;base64,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" style="width: 59px; height: 18.5px;" width="59" height="18.5"></span><span style="block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 36.5px 8px; transform-origin: 36.5px 8px; unicode-bidi: normal; "><span style="">. Given the nth element </span></span><span style="vertical-align:-5px"><img src="data:image/png;base64,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" style="width: 33px; height: 18.5px;" width="33" height="18.5"></span><span style="block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 134.5px 8px; transform-origin: 134.5px 8px; unicode-bidi: normal; "><span style="">, find the value of the corresponding index </span></span><span style="font-family: &quot;STIXGeneral&quot;, &quot;STIXGeneral-webfont&quot;, serif; font-style: italic; font-weight: 400; color: rgb(0, 0, 0);">n</span><span style="block-size: auto; display: inline; margin-block-end: 0px; margin-block-start: 0px; margin-bottom: 0px; margin-inline-end: 0px; margin-inline-start: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; perspective-origin: 2px 8px; transform-origin: 2px 8px; unicode-bidi: normal; "><span style="">.</span></span></div></div></div>

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205 Solutions
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Last Solution submitted on Mar 13, 2023

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Dyuman Joshi on 10 Aug 2021

@Ramon, if you are submitting a question on Cody for everybody to solve, it is recommended you put atleast 3 test suites, mostly so that it encourages people to learn and not hard code solutions.

Ramon Villamangca on 11 Aug 2021

Thanks, @Dyuman. There are now 4 test suites.

Dyuman Joshi on 11 Aug 2021

@Ramon, Wonderful!

David Hill on 12 Aug 2021

-a+(1-(-1)^(n+1))/2 will be negative in the 4th test. I believe it should be: index(a-(1-(-1)^(n+1))/2).

Rahul Gulia on 24 Sep 2021

This works fine in my MATLAB software. But not here.
Any comments, please?

function n = index(a)
for idx = 1:1000
b = idx*((-1)^(idx^3+1));
if b==a
break
else
continue
end
end
n=idx;
end

Dyuman Joshi on 24 Sep 2021

Because you are not doing what the question is asking

Asif Newaz on 21 Aug 2022

I think the last test case is wrong

Rafael S.T. Vieira on 12 Nov 2022

Rahul Gulia, in the last test, there will be numbers greater than 1000. And the last test is not wrong. Just remember that indexes are always positive (I had trouble with that also, we are so focused on the sequence that we forget that indexes can't be negative).

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Problem 52462. Easy Sequences 1: Find the index of an element

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Problem 52462. Easy Sequences 1: Find the index of an element

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