Solution2.java

class Solution {
    private static final int INF = 0x3f3f;

    public int networkDelayTime(int[][] times, int n, int k) {
        List<int[]>[] g = new List[n];
        int[] dist = new int[n];
        for (int i = 0; i < n; ++i) {
            dist[i] = INF;
            g[i] = new ArrayList<>();
        }
        for (int[] t : times) {
            g[t[0] - 1].add(new int[] {t[1] - 1, t[2]});
        }
        dist[k - 1] = 0;
        PriorityQueue<int[]> q = new PriorityQueue<>(Comparator.comparingInt(a -> a[0]));
        q.offer(new int[] {0, k - 1});
        while (!q.isEmpty()) {
            int[] p = q.poll();
            int u = p[1];
            for (int[] ne : g[u]) {
                int v = ne[0], w = ne[1];
                if (dist[v] > dist[u] + w) {
                    dist[v] = dist[u] + w;
                    q.offer(new int[] {dist[v], v});
                }
            }
        }
        int ans = 0;
        for (int d : dist) {
            ans = Math.max(ans, d);
        }
        return ans == INF ? -1 : ans;
    }
}