Network Delay Time

There are N network nodes, labelled 1 to N.

Given times, a list of travel times as directed edges times[i] = (u, v, w), where u is the source node, v is the target node, and w is the time it takes for a signal to travel from source to target.

Now, we send a signal from a certain node K. How long will it take for all nodes to receive the signal? If it is impossible, return -1.

Example 1:

Input: times = [[2,1,1],[2,3,1],[3,4,1]], N = 4, K = 2
Output: 2

Note:

1. N will be in the range [1, 100].

2. K will be in the range [1, N].

3. The length of times will be in the range [1, 6000].

4. All edges times[i] = (u, v, w) will have 1 <= u, v <= N and 0 <= w <= 100.

class Solution {
    public int networkDelayTime(int[][] times, int N, int K) {
        // Creating Adjacency List
        ArrayList<int[]>[] graph = new ArrayList[N];
        for (int i = 0; i < N; i++)
            graph[i] = new ArrayList<>();
        for (int[] edge : times)
            graph[edge[0] - 1].add(new int[] { edge[1] - 1, edge[2] });

        // (distance, node) into pq
        PriorityQueue<int[]> pq = new PriorityQueue<>((a, b) -> (a[0] - b[0]));
        pq.add(new int[] { 0, K - 1 });

        boolean[] visited = new boolean[N];
        int res = 0, coveredNodes = 0;
        while (!pq.isEmpty()) {
            // Picking the Node at shortest Distance
            int[] cur = pq.remove();
            int curDist = cur[0];
            int curNode = cur[1];
            if (visited[curNode])
                continue;
            visited[curNode] = true;
            // The last node in the PQ will have the largest distance already
            res = curDist;
            coveredNodes++;
            for (int[] node : graph[curNode])
                pq.add(new int[] { curDist + node[1], node[0] });
        }
        return coveredNodes == N ? res : -1;
    }
}