AoC 2021 D15: Chiton

| Problem statement | Source code | Tags: Dijkstra

This is a classic shortest path problem, where the edge weights are the risk levels of the destination cells. I just run Dijkstra's. I never remember how to write one, and Wikipedia's first version is the non-ideal one, so here's a better template:

function dijkstra(grid: number[][]): number {
  const width = grid[0].length;
  const height = grid.length;
  const dist = Array.from({ length: height }, () =>
    Array.from({ length: width }, () => Infinity),
  );
  dist[0][0] = 0;
  const pq = new MinPriorityQueue<[number, number]>();
  pq.enqueue([0, 0], 0);
  while (!pq.isEmpty()) {
    const { priority, element } = pq.dequeue() as PriorityQueueItem<
      [number, number]
    >;
    for (const [nx, ny] of neighbors(element[0], element[1], width, height)) {
      const newCost = priority + grid[ny][nx];
      if (newCost < dist[ny][nx]) {
        dist[ny][nx] = newCost;
        pq.enqueue([nx, ny], newCost);
      }
    }
  }
  return dist[height - 1][width - 1];
}

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