2023 Day 16

2023/16/run.ts

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+/**
+ * Day 16: The Floor Will Be Lava
+ * https://adventofcode.com/2023/day/16
+ */
+
+console.time("Run time");
+
+import fs from "fs";
+
+enum DIRECTION {
+    UP = 0,
+    RIGHT = 1,
+    DOWN = 2,
+    LEFT = 3
+};
+
+const grid: string[][] = fs.readFileSync("./16/input.txt", "utf-8")
+    .split(/[\r\n]+/)
+    .map(row => row.trim())
+    .filter(Boolean)
+    .map(row => row.split(""));
+
+console.info("Part 1: " + solve([[-1, 0, DIRECTION.RIGHT]]));
+
+// Part 2
+let highestConfiguration = 0;
+
+// Top and bottom rows
+for (let x = 0; x < grid[0].length; x++) {
+    const resultTop = solve([[x, -1, DIRECTION.DOWN]]);
+    if (resultTop > highestConfiguration) {
+        highestConfiguration = resultTop;
+    }
+
+    const resultBottom = solve([[x, grid.length, DIRECTION.UP]]);
+    if (resultBottom > highestConfiguration) {
+        highestConfiguration = resultBottom;
+    }
+}
+
+// Right and left columns
+for (let y = 0; y < grid.length; y++) {
+    const resultRight = solve([[-1, y, DIRECTION.RIGHT]]);
+    if (resultRight > highestConfiguration) {
+        highestConfiguration = resultRight;
+    }
+
+    const resultLeft = solve([[grid[y].length, y, DIRECTION.LEFT]]);
+    if (resultLeft > highestConfiguration) {
+        highestConfiguration = resultLeft;
+    }
+}
+
+console.info("Part 2: " + highestConfiguration);
+
+console.timeEnd("Run time");
+
+/**
+ * @param beams [x, y, direction]
+ */
+function solve(beams: number[][]): number {
+    const visited: Set<string> = new Set();
+    const energized: Set<string> = new Set();
+
+    while (beams.length) {
+        for (let i = beams.length - 1; i >= 0; i--) {
+            const beam = beams[i];
+
+            // Move
+            switch (beam[2]) {
+                case DIRECTION.UP: beam[1]--; break;
+                case DIRECTION.RIGHT: beam[0]++; break;
+                case DIRECTION.DOWN: beam[1]++; break;
+                case DIRECTION.LEFT: beam[0]--; break;
+                default: throw new Error(`Invalid direction ${beam[2]}`);
+            }
+
+            // Outside grid => destroy
+            // Already visited in this direction => destroy
+            if (beam[0] < 0 || beam[0] >= grid[0].length || beam[1] < 0 || beam[1] >= grid.length || visited.has(beam.join(","))) {
+                beams.splice(i, 1);
+                continue;
+            }
+
+            visited.add(beam.join(","));
+            energized.add([beam[0], beam[1]].join(","));
+
+            // Switch direction and split
+            switch (grid[beam[1]][beam[0]][0]) {
+                case ".": break;
+                case "/":
+                    switch (beam[2]) {
+                        case DIRECTION.UP: beam[2] = DIRECTION.RIGHT; break;
+                        case DIRECTION.RIGHT: beam[2] = DIRECTION.UP; break;
+                        case DIRECTION.DOWN: beam[2] = DIRECTION.LEFT; break;
+                        case DIRECTION.LEFT: beam[2] = DIRECTION.DOWN; break;
+                    }
+                    break;
+                case "\\":
+                    switch (beam[2]) {
+                        case DIRECTION.UP: beam[2] = DIRECTION.LEFT; break;
+                        case DIRECTION.RIGHT: beam[2] = DIRECTION.DOWN; break;
+                        case DIRECTION.DOWN: beam[2] = DIRECTION.RIGHT; break;
+                        case DIRECTION.LEFT: beam[2] = DIRECTION.UP; break;
+                    }
+                    break;
+                case "|":
+                    switch (beam[2]) {
+                        case DIRECTION.RIGHT:
+                        case DIRECTION.LEFT:
+                            beam[2] = DIRECTION.UP;
+                            beams.push([beam[0], beam[1], DIRECTION.DOWN]);
+                    }
+                    break;
+                case "-":
+                    switch (beam[2]) {
+                        case DIRECTION.UP:
+                        case DIRECTION.DOWN:
+                            beam[2] = DIRECTION.LEFT;
+                            beams.push([beam[0], beam[1], DIRECTION.RIGHT]);
+                    }
+                    break;
+                default: throw new Error(`Invalid character ${grid[beam[1]][beam[0]][0]}`);
+            }
+        }
+    }
+
+    return energized.size;
+}