day 10 part 2

Author: RomanSixty

10/solve.js

@@ -1,12 +1,66 @@
 adventofcode.activate(10);
 
-adventofcode.day10_asteroids = [];
-
 adventofcode.day10_part1 = function(input) {
     adventofcode.day10_asteroids = [];
 
     adventofcode.day10_get_asteroids(input);
 
+    return adventofcode.day10_max_seeing;
+};
+
+adventofcode.day10_part2 = function(input) {
+    adventofcode.day10_asteroids = [];
+
+    adventofcode.day10_get_asteroids(input);
+
+    // lets just sort all the y/x fractions of the best asteroid clockwise
+    // the order is as follows:
+    //   -∞ -> +∞ for positive x, then
+    //   -∞ -> +∞ for negative x
+    let list = adventofcode.day10_asteroids[adventofcode.day10_best_asteroid].losFractions.sort(function(a, b){
+        // divisions by 0 suck... hence
+        if (a[0] === 0)
+            a[0] = 0.0001;
+
+        if (b[0] === 0)
+            b[0] = 0.0001;
+
+        if (a[0] > 0) {
+            if (b[0] > 0)
+                return (a[1]/a[0] > b[1]/b[0]);
+            else
+                return -1;
+        } else {
+            if (b[0] < 0)
+                return (a[1]/a[0] > b[1]/b[0]);
+            else
+                return 1;
+        }
+    });
+
+    // also we're lucky knowing we found more than 200 asteroids on first sight
+    // so the laser doesn't have to wrap around and we don't need to calculate
+    // all newly visible asteroids again
+
+    const asteroid_200 = adventofcode.day10_asteroids[list[199][2]];
+
+    return ( asteroid_200.x * 100 + asteroid_200.y);
+};
+
+adventofcode.day10_get_asteroids = function(input) {
+    input.split("\n").forEach((data, row) => {
+        data.split("").forEach((value, col) => {
+            if (value === '#') {
+                adventofcode.day10_asteroids.push({
+                    x: col,
+                    y: row,
+                    seeing: 0,       // number of other asteroids we see
+                    losFractions: [] // line of sight fractions and id of asteroid as third value
+                });
+            }
+        });
+    });
+
     adventofcode.day10_asteroids.forEach((asteroid1, nr1) => {
         adventofcode.day10_asteroids.forEach((asteroid2, nr2) => {
             // don't check against ourself
@@ -29,37 +83,20 @@ adventofcode.day10_part1 = function(input) {
                 adventofcode.day10_asteroids[nr1].seeing++;
                 adventofcode.day10_asteroids[nr2].seeing++;
 
-                adventofcode.day10_asteroids[nr1].losFractions.push([diff_x, diff_y]);
-                adventofcode.day10_asteroids[nr2].losFractions.push([-diff_x, -diff_y]);
+                adventofcode.day10_asteroids[nr1].losFractions.push([diff_x, diff_y,   nr2]);
+                adventofcode.day10_asteroids[nr2].losFractions.push([-diff_x, -diff_y, nr1]);
             }
         });
     });
 
-    let max_seeing = 0;
-
-    adventofcode.day10_asteroids.forEach(asteroid => {
-        max_seeing = Math.max(asteroid.seeing, max_seeing);
-    });
-
-    return max_seeing;
-};
-
-adventofcode.day10_part2 = function(input) {
-    return 'maybe tomorrow';
-};
+    adventofcode.day10_max_seeing    = 0;
+    adventofcode.day10_best_asteroid = 0;
 
-adventofcode.day10_get_asteroids = function(input) {
-    input.split("\n").forEach((data, row) => {
-        data.split("").forEach((value, col) => {
-            if (value === '#') {
-                adventofcode.day10_asteroids.push({
-                    x: col,
-                    y: row,
-                    seeing: 0,       // number of other asteroids we see
-                    losFractions: [] // line of sight fractions
-                });
-            }
-        });
+    adventofcode.day10_asteroids.forEach((asteroid, nr) => {
+        if (adventofcode.day10_max_seeing < asteroid.seeing) {
+            adventofcode.day10_max_seeing = asteroid.seeing;
+            adventofcode.day10_best_asteroid = nr;
+        }
     });
 };