CODEWITHSUNDEEP
javascriptlogic
ajax333221
ajax333221

Reputation: 11774

How to rewrite a negated line?

Negating takes me hours of trial and error until nothing breaks, any method of negating other than intuitively? For example:

//x and y are whole numbers

!((x<9) && (y<=(8-x)))
((x>8) || (y>(8-x)))

Upvotes: 0

Views: 52

Answers (1)

Scott Sauyet
Scott Sauyet

Reputation: 50807

The simplest thing is to ignore questions about the domain of values, and treat this as an entirely logical problem. Then we can break it down into cases such as:

!(A || B) ~= !A && !B
!(A && B) ~= !A || !B
!(!A) ~= A
!(x > y) ~= x <= y
!(x >= y) ~= x < y

The first two can easily be extended:

!(A || B || C || D || ...) ~= !A && !B && !C && !D && ...
!(A && B && C && D && ...) ~= !A || !B || !C || !D || ...

So, for one of your examples, we have:

!((x < 9) && (y <= (8 - x)))
!(x < 9) || !(y <= (8 - x))
(x >= 9) || (y > (8 - x))

We could leave it as this, but as you had additional domain information, ("x and y are whole numbers"), you might incorporate it to return a slightly less specific, but accurate enough in context answer, such as

(x > 8) || (y > (8 - x))

You would have to decide on a case-by-case basis whether this is worth the additional steps. What it might gain is a somewhat reduced codebase, it can also lose in a less transparent link to the original format.

Upvotes: 2

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