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README.md

04 - Santa's radians

Description

Level: Easy
Author: dr_nick

Santa, who is a passionate mathematician, has created a small website to train his animation coding skills. Although Santa lives in the north pole, where the degrees are very low, the website's animation luckily did not freeze. It just seems to move very slooowww. But how does this help...? The elves think there might be a flag in the application...

Solution

For this challenge we are given a website what displays half-open circles:

website.png

Looking at the source, we can see some rotations in an array:

let rot = [2.5132741228718345, 0.4886921905584123, -1.2566370614359172, 0, 2.548180707911721, -1.9547687622336491, -0.5235987755982988, 1.9547687622336491, -0.3141592653589793, 0.6283185307179586, -0.3141592653589793, -1.8151424220741028, 1.361356816555577, 0.8377580409572781, -2.443460952792061, 2.3387411976724013, -0.41887902047863906, -0.3141592653589793, -0.5235987755982988, -0.24434609527920614, 1.8151424220741028];

I converted the rotations to degrees:

rot.map(e => e *180/Math.PI)

which gave me the array:

[144,28,-72,0,146,-112,-29.999999999999996,112,-18,36,-18,-104.00000000000001,78,48,-140,133.99999999999997,-24,-18,-29.999999999999996,-14,104.00000000000001]

The ascii value of V is 72, which is exactly half of what we got. Because of this, I divided all the elements by 2 and got:

[72,14,-36,0,73,-56,-15,56,-9,18,-9,-52,39,24,-70,67,-12,-9,-15,-7,52]

At this point I got stuck for a while. Only the first letter was correct and the rest didn't make up a readable flag. The second value should be 86 if we assume the normal flag format starting with HV. Doing a prefix sum of the elements, however, gave the correct array:

for (let i = 0; i < rot.length; i++) {
    let sum = 0;
    for (let j = 0; j <= i; j++) {
        sum += rot[j];
    }
    console.log(String.fromCharCode(sum));
}

And this finally prints: HV22{C4lcul8_w1th_PI}.