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Advent of Code: 2023 Day 18
function parse(input) {
return input.split("\n").map((instr) => {
const [, dir, len] = instr.match(/([UDLR])\s+(\d+)/);
return { dir: dir, len: Number(len) };
});
}
function toPoly(instrs) {
const vertices = [[0, 0]];
let [x, y] = [0, 0];
instrs.forEach((v) => {
switch (v.dir) {
case "L":
x -= v.len;
break;
case "R":
x += v.len;
break;
case "U":
y -= v.len;
break;
case "D":
y += v.len;
break;
}
vertices.push([x, y]);
});
return vertices;
}
function polyData(instrs) {
const polygon = toPoly(instrs);
const area = Math.abs(d3.polygonArea(polygon)); // abs so we can ignore winding order.
const perimeter = AOC.sum(instrs.map((d) => d.len));
return {
polygon: polygon,
perimeter: perimeter,
area: area,
griddedArea: area + perimeter / 2 + 1
};
}
function part1(input) {
return polyData(parse(input)).griddedArea;
}
function parse2(input) {
const hexToInstr = (hex) => {
const len = parseInt(hex.slice(2, -2), 16);
let dir;
switch (hex.slice(-2, -1)) {
case "0":
dir = "R";
break;
case "1":
dir = "D";
break;
case "2":
dir = "L";
break;
case "3":
dir = "U";
break;
}
return { dir: dir, len: len };
};
return input.split("\n").map((line) => hexToInstr(line.split(/\s+/)[2]));
}
function part2(input) {
return polyData(parse2(input)).griddedArea;
}
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