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Challenges

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Negabinary means base negative two (-2). That is, the $n$th place value is determined by $(-2)^n$.

Negabinary numbers can be evaluated just like any other base system. For example, we can parse the numbers 101, 110, and 1010 as follows:

-8 4 -2 1 value
1 0 1 5
1 1 0 2
1 0 1 0 -10

## Challenge

Given two negabinary integers, output the sum of them in negabinary.

You may take inputs in any format that makes sense. However, the output of the function/program must be in the same format as the input

The following ungolfed example takes in two 0-indexed arrays, with the nth entry being the nth place of each number.

let carry = 0;
let result = [];

let place = 0;
while(place < first.length || place < second.length || carry) {
let num = (first[place] || 0) + (second[place] || 0) + carry;
let bit;
switch (num) {
case -1: bit = 1; carry = 1; break;
case 0: bit = 0; carry = 0; break;
case 1: bit = 1; carry = 0; break;
case 2: bit = 0; carry = -1; break;
case 3: bit = 1; carry = -1; break;
}
result.push(bit);
place++;
}
return result;
}

Try it online!

## Some test cases

1 + 0 = 1
1 + 1 = 110        // 1 + 1 = 2
1 + 110 = 111      // 1 + 2 = 3
10 + 1 = 11        // -2 + 1 = -1
10 + 1011 = 110101 // -2 + -9 = -11

1010101 + 1110100 = 110011001
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# Jelly, 6 bytes

ḅSbɗ-2

Try it online!

Takes input and output as a pair of lists of digits. The Footer converts to and from.

Jelly's generalised base conversion works for all integer bases, and allows converting from complex bases.

## How it works

ḅSbɗ-2 - Main link. Takes [a, b] on the left
ḅ      -   Convert from base -2
S     -   Sum
b    -   Convert to base -2
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# Japt, 8 bytes

Input as an array of negabinary digit arrays, output as a negabinary digit array.

xì2n)ì2n

Try it or run all test cases (headers & footers convert to & from digit arrays)

xì2n)ì2n      :Implicit input of 2D digit array
ì            :  Converting each from base
2n          :  -2
)         :End reduce
ì2n      :Convert to base -2 digit array
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# Ruby, 75 bytes

->t,u{g=->a{a.reduce{-2*_1+_2}};('%b'%(g[t]+g[u]+(y=43690)^y)).to_i.digits}

Try it online!

Uses latest ruby features, so tio link will look different.

Takes two digit arrays, and returns an array which represents the negabinary integer.

Borrows from a conversion technique used here.

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