2024 day 10 part 2 in javascript

2024/10/solution2.js

@@ -0,0 +1,55 @@
+
+const input = (await Bun.file("input.txt").text()).trim()
+
+const rows = [[]];
+
+const trailheads = [];
+
+for (let i = 0, x = 0, y = 0; i < input.length; i++) {
+  if (input[i] == "\n") {
+    rows.push([]);
+    y++;
+    x = 0;
+    continue;
+  }
+  const alt = parseInt(input[i]);
+  rows[y].push(alt);
+  if (alt == 0) {
+    trailheads.push({x,y})
+  }
+  x++;
+}
+
+const summitChart = Array.from({length: rows.length}, () => Array.from({length: rows.length}, () => ([])))
+
+function findSummits({x, y}) {
+  if (summitChart[y][x].length > 0) {
+    return summitChart[y][x]
+  }
+  if (rows[y][x] == 9) {
+    summitChart[y][x].push(x + y * rows.length)
+    return summitChart[y][x]
+  }
+  if (x != 0               && rows[y][x-1] - rows[y][x] == 1) {
+    summitChart[y][x].push(...findSummits({y, x: x - 1}))
+  }
+  if (x != rows.length - 1 && rows[y][x+1] - rows[y][x] == 1) {
+    summitChart[y][x].push(...findSummits({y, x: x + 1}))
+  }
+  if (y != 0               && rows[y-1][x] - rows[y][x] == 1) {
+    summitChart[y][x].push(...findSummits({y: y-1, x}))
+  }
+  if (y != rows.length - 1 && rows[y+1][x] - rows[y][x] == 1) {
+    summitChart[y][x].push(...findSummits({y: y+1, x}))
+  }
+  return summitChart[y][x]
+}
+
+let sum = 0;
+for (const trailhead of trailheads) {
+  const summits = findSummits(trailhead)
+  sum += summits.length
+}
+
+console.log(sum)
+