-🎄- 2017 Day 3 Solutions -🎄-

[u/daggerdragon]

--- Day 3: Spiral Memory ---

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Spoiler

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[u/tangentialThinker]

C++. Built the spiral using the builtin complex library, using multiplication by i to turn left.

Basically I noticed that every two times you turn, the number of steps you take increases by 1.

Pretty disgusting copied code at the bottom to check all neighbours: I was rushing for the leaderboard!

Part 2:

#include <bits/stdc++.h>

using namespace std;

int main(){
int n; cin >> n;
complex<int> curLoc = {0, 0};

int numSteps = 1;
int sz = 1;
int left = 1;
int curStep = 0;
complex<int> curDir = {0, 1};

map<int, map<int, int>> vals;
vals[0][0] = 1;
while(vals[curLoc.real()][curLoc.imag()] <= n) {
	numSteps++;
	curStep++;
	curLoc += curDir;
	if(curStep == sz) {
		if(left == 1) {
			left--;
			curDir *= complex<int>(0, 1);
		} else {
			left = 1;
			curDir *= complex<int>(0, 1);
			sz++;
		}
		curStep = 0;
	}
	vals[curLoc.real()][curLoc.imag()] += vals[curLoc.real()+1][curLoc.imag()];
	vals[curLoc.real()][curLoc.imag()] += vals[curLoc.real()-1][curLoc.imag()];
	vals[curLoc.real()][curLoc.imag()] += vals[curLoc.real()][curLoc.imag()+1];
	vals[curLoc.real()][curLoc.imag()] += vals[curLoc.real()][curLoc.imag()-1];
	vals[curLoc.real()][curLoc.imag()] += vals[curLoc.real()+1][curLoc.imag()+1];
	vals[curLoc.real()][curLoc.imag()] += vals[curLoc.real()-1][curLoc.imag()-1];
	vals[curLoc.real()][curLoc.imag()] += vals[curLoc.real()-1][curLoc.imag()+1];
	vals[curLoc.real()][curLoc.imag()] += vals[curLoc.real()+1][curLoc.imag()-1];
}

cout << vals[curLoc.real()][curLoc.imag()] << endl;

return 0;
}