feat(day_8): part B done

src/exercises/day_8.ts

@@ -12,6 +12,10 @@ export default async function Playground() {
     ">> Three largest pairings mul: ",
     get_three_largest_pairings_mul(junction_boxes_coords, 1000),
   );
+  console.log(
+    ">> Last pairing mul: ",
+    get_last_pairing_mul(junction_boxes_coords),
+  );
 }
 
 export function get_three_largest_pairings_mul(
@@ -28,11 +32,26 @@ export function get_three_largest_pairings_mul(
   return total;
 }
 
+export function get_last_pairing_mul(box_list: Coordinate[]): number {
+  const last_pairing = get_last_pairing_circuit(box_list);
+  if (last_pairing) {
+    return box_list[last_pairing.a].x * box_list[last_pairing.b].x;
+  }
+  return 0;
+}
+
+interface DistancePairing {
+  a: number;
+  b: number;
+  distance: number;
+}
+
 function generate_n_shortest_distances(
   box_list: Coordinate[],
   n: number,
-): { a: number; b: number; distance: number }[] {
-  const distances: { a: number; b: number; distance: number }[] = [];
+  initial_distances?: DistancePairing[],
+): DistancePairing[] {
+  const distances: DistancePairing[] = initial_distances ?? [];
   for (let i = 0; i < n; i++) {
     const shortest_distance: { distance: number; pair_index: number[] } = {
       distance: Infinity, // Dirty, but it's late
@@ -86,73 +105,52 @@ function generate_n_shortest_pairings(
   return circuits;
 }
 
-function _generate_n_shortest_pairings(
+function get_last_pairing_circuit(
   box_list: Coordinate[],
-  max_pairings: number,
-): number[][] {
-  const circuits: number[][] = [];
-  const pairings: number[][] = [];
+): DistancePairing | undefined {
+  const INCREMENT = 10; // NOTE: to adjust computation cost, since the solution is inefficient
+  const circuits: number[][] = box_list.map((_, i) => [i]);
 
-  // Pair generation
-  for (let i = 0; i < max_pairings; i++) {
-    const shortest_distance: { distance: number; pair_index: number[] } = {
-      distance: Infinity, // Dirty, but it's late
-      pair_index: [],
-    };
-
-    // Pair boxes
-    box_list.forEach((box, box_index) => {
-      for (let next_i = box_index + 1; next_i < box_list.length; next_i++) {
-        const next_box = box_list[next_i];
-        const next_distance = calc_distance(box, next_box);
-        if (
-          next_distance < shortest_distance.distance &&
-          !pairings.some((pairing) =>
-            pairing.includes(box_index) && pairing.includes(next_i)
-          )
-        ) {
-          shortest_distance.distance = next_distance;
-          shortest_distance.pair_index = [box_index, next_i];
+  const is_done = (c: number[][]): boolean => {
+    return c.reduce((prev, current) => {
+        if (current.length > 0) {
+          return prev + 1;
         }
+        return prev;
+      }, 0) > 1
+      ? false
+      : true;
+  };
+
+  let last_pairing: DistancePairing | undefined;
+
+  let distance_list = generate_n_shortest_distances(box_list, INCREMENT);
+  while (!is_done(circuits)) {
+    distance_list = generate_n_shortest_distances(
+      box_list,
+      INCREMENT,
+      distance_list,
+    );
+    distance_list.forEach((distance) => {
+      const a = circuits.find((c) => c.includes(distance.a));
+      const b = circuits.find((c) => c.includes(distance.b));
+
+      if (a?.length && b?.length && a !== b) {
+        last_pairing = {
+          a: distance.a,
+          b: distance.b,
+          distance: distance.distance,
+        };
+        const to_empty_index = circuits.findIndex((c) =>
+          c.includes(distance.b)
+        );
+        b.forEach((x) => a.push(x));
+        circuits[to_empty_index] = [];
       }
     });
-    // Update paring list
-    pairings.push(shortest_distance.pair_index);
-    // Check shortest pairings and then push
-    const a_circiut = circuits.find((c) =>
-      c.includes(shortest_distance.pair_index[0])
-    );
-    const b_circiut = circuits.find((c) =>
-      c.includes(shortest_distance.pair_index[1])
-    );
-
-    if (
-      a_circiut && b_circiut
-    ) {
-      const n_index = circuits.findIndex((p) =>
-        p.includes(shortest_distance.pair_index[1])
-      );
-      b_circiut.forEach((b) => {
-        circuits.find((p) => p.includes(shortest_distance.pair_index[0]))
-          ?.push(b);
-      });
-      circuits[n_index] = [];
-    } else if (
-      a_circiut
-    ) {
-      circuits.find((p) => p.includes(shortest_distance.pair_index[0]))
-        ?.push(shortest_distance.pair_index[1]);
-    } else if (
-      b_circiut
-    ) {
-      circuits.find((p) => p.includes(shortest_distance.pair_index[1]))
-        ?.push(shortest_distance.pair_index[0]);
-    } else {
-      circuits.push(shortest_distance.pair_index);
-    }
   }
 
-  return circuits;
+  return last_pairing;
 }
 
 function calc_distance(a: Coordinate, b: Coordinate): number {