2021.05

challenges/2021/05.js

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+// Part 1
+const solvePuzzle1 = (input) => {
+  const [lines, diagram] = parseInput(input);
+  return findOverlaps(lines.filter(isHorizontalOrVertical), diagram).size;
+};
+
+// Part 2
+const solvePuzzle2 = (input) => {
+  const [lines, diagram] = parseInput(input);
+  return findOverlaps(lines, diagram).size;
+};
+
+const parseInput = (input) => {
+  let [maxX, maxY] = [0, 0];
+
+  input = input.split("\n").map((line) =>
+    line.split(" -> ").map((xy) =>
+      xy.split(",").map((n, idx) => {
+        n = Number(n);
+        if (idx > 0) {
+          maxY = Math.max(maxY, n);
+        } else {
+          maxX = Math.max(maxX, n);
+        }
+        return n;
+      })
+    )
+  );
+
+  const diagram = Array.from({ length: maxY + 1 }, () => new Array(maxX + 1).fill(0));
+
+  return [input, diagram];
+};
+
+const findOverlaps = (lines, diagram) => {
+  let overlaps = new Set();
+  lines.forEach((line) => {
+    const [[x1, y1], [x2, y2]] = line;
+
+    const minX = Math.min(x1, x2);
+    const maxX = Math.max(x1, x2);
+    const minY = Math.min(y1, y2);
+    const maxY = Math.max(y1, y2);
+    const increasingX = minX < maxX;
+    const decreasingY = isGoingNE(line);
+    const increasingY = !decreasingY && minY < maxY;
+    let x = minX;
+    let y = decreasingY ? maxY : minY;
+
+    while (x <= maxX && y <= maxY && y >= minY) {
+      diagram[y][x]++;
+      diagram[y][x] > 1 && overlaps.add(`${y},${x}`);
+      increasingX && x++;
+      increasingY && y++;
+      decreasingY && y--;
+    }
+  });
+  return overlaps;
+};
+
+const isHorizontal = ([[_, y1], [__, y2]]) => y1 === y2;
+const isVertical = ([[x1, _], [x2, __]]) => x1 === x2;
+const isHorizontalOrVertical = (line) => isHorizontal(line) || isVertical(line);
+const isDiagonal = (line) => !isHorizontalOrVertical(line);
+const isGoingNE = (line) => {
+  const [[x1, y1], [x2, y2]] = line;
+  return (isDiagonal(line) && x1 < x2 && y1 > y2) || (y1 < y2 && x1 > x2);
+};
+
+require(__dirname + "/../../utils/test.js").test(__filename, __dirname, solvePuzzle1);
+require(__dirname + "/../../utils/test.js").test(__filename, __dirname, solvePuzzle2);