Sum of alternate numbers in Java

posted 5 years ago

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I'm having trouble understanding/figuring out how i'm supposed to code the alternating sum of an inputed number /I suppose as in int??/

The code is supposed to take a number lets say 4321 and alternate + and - between the numbers. It can start either with - or + which really throws me off

there are 2 shown inputs and expected outputs as an example:
input1= 101 => output1= 2 , we take  +1-0+1=2
input2= 42 => output2= -2 , which should mean we take the first number as "-" => -4+2=-2

I'm really in a pinch here and i've got no idea what to do ;/

Saloon Keeper

Posts: 5141

posted 5 years ago

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There are three kinds of actuaries: those who can count, and those who can't.

Petar Stoyanov

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posted 5 years ago

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As far as i can see he has the expected output and must figure out what signs to have between 1,2,3,4,5,6... to get to that expected output the fastest
i just have random input numbers 231,412,51... and can get 2 outputs basicly - 1 starting from + then - and alternating or starting from - and then + and so on.
I have to brake down a number ex. 231 into 2,3,1 and then alternate +,- between them

Ranch Hand

Posts: 109

posted 5 years ago

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My two cents as a beginner in programming.

Input 1 takes 1234.
Do while number is not 0
{1234%10=4.
Store 4 in the array with length arraylength=(int)(Math.log10(n)+1).
1234=1234/10}
for(i=0;i<arraylength;i++)
//create a sum where you alternate the sign using a variable which assigns itself - for iteration 1 and back to + to iteration 2.

Do almost the same for the second output.

posted 5 years ago

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To alternate the sign, use these basic math facts:

If you have a variable,

, you can easily flip it between -1 and +1 using the above.

Marshal

Posts: 76727

posted 5 years ago

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You can “randomly” start with a different sign like this:-The () are redundant, but it is often worth using () around ?: because it has a low precedence. Another way to swap signs is like this:-The () are again redundant.

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