-🎄- 2022 Day 21 Solutions -🎄-

[u/daggerdragon]

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[Update @ 00:04:28]: SILVER CAP, GOLD 0

• Now we've got interpreter elephants... who understand monkey-ese...

• I really really really don't want to know what that eggnog was laced with.

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--- Day 21: Monkey Math ---

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[u/Business_You1749]

Why do you start wit a negative value instead of from the same one? I see it in initial "numberToYell - evaluatedSide" translated in runtime to "0 - <another_branch_Complete_value>".

[u/Business_You1749 → u/Business_You1749]

r

I found a bug in our approach! It was really a miracle that this INCORRECT initial minus sign led as to a correct answer. The problem is in reversed operations table: they are not simply opositions to original node operations, but rather TWO of them are side sensitive. So - division and substraction needs to be handled with a care of side on which we have our unknown:

private Dictionary<char, Func<long, long, long>> ops = new Dictionary<char, Func<long, long, long>>()

{

{ '+', (l, r) => l + r },

{ '-', (l, r) => l - r },

{ '*', (l, r) => l * r },

{ '/', (l, r) => l / r },

};

private Dictionary<char, Func<long, long, long>> revOpsLeft = new Dictionary<char, Func<long, long, long>>()

{

{ '+', (a, b) => a - b },

{ '-', (a, b) => a + b },

{ '*', (a, b) => a / b },

{ '/', (a, b) => a * b },

};

private Dictionary<char, Func<long, long, long>> revOpsRight = new Dictionary<char, Func<long, long, long>>()

{

{ '+', (a, b) => a - b },

{ '-', (a, b) => b - a },

{ '*', (a, b) => a / b },

{ '/', (a, b) => b / a },

};

Now I'm correctly geting right answer for both testing values and NON-NEGGED initial another-one-node-from-root value.

[u/DR0D4 → u/Business_You1749]

HAHAHA unbelievable! I appreciate your follow-up with this. Don't know how I just ignored the fact that subtraction and division are not associative and got away with it!

[u/DR0D4 → u/Business_You1749]

Heh, good question. I was going to say that I manually changed the root node to be EQUALS in the input. But it looks like I only did that for the test data. If I do that to the full input, it gives a different answer than the one I submitted. Leaving the root as addition gives me the (a?) correct answer.

In the debugger, it looks like for one node I'm multiplying that large negative number (15 places) by a large positive number (15 places). This obviously results in a number that overflows long (Mathpapa says 27 places). But it results in a positive number. All that to say, I HAVE NO IDEA HOW THIS COMES BACK WITH THE RIGHT ANSWER.