Dijkstra（堆優化）

import java.util.Comparator;
import java.util.PriorityQueue;
import java.util.Scanner;

/**
 * O（m * log(n)）
 */
public class Main {

    private static final int INF = Integer.MAX_VALUE;

    static class Item {
        int no;
        int dist;

        public Item(int no, int dist) {
            this.no = no;
            this.dist = dist;
        }
    }

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        while (in.hasNext()) {
            int n = in.nextInt();
            int m = in.nextInt();

            int edgeIndex = 0;
            int[] lastEdge = new int[n + 1];

            int[] weight = new int[m + 1];
            int[] end = new int[m + 1];
            int[] previousEdge = new int[m + 1];

            while (m -- > 0) {
                int a = in.nextInt();
                int b = in.nextInt();
                int c = in.nextInt();

                ++ edgeIndex;
                weight[edgeIndex] = c;
                end[edgeIndex] = b;
                previousEdge[edgeIndex] = lastEdge[a];
                lastEdge[a] = edgeIndex;
            }

            int[] dist = new int[n + 1];
            dist[1] = 0;

            for (int i = 2; i <= n; ++ i) {
                dist[i] = INF;
            }

            PriorityQueue<Item> queue = new PriorityQueue<>(new Comparator<Item>() {
                @Override
                public int compare(Item o1, Item o2) {
                    return o1.dist - o2.dist;
                }
            });

            queue.add(new Item(1, 0));

            while (! queue.isEmpty()) {
                Item top = queue.poll();

                for (int i = lastEdge[top.no]; i != 0; i = previousEdge[i]) {

                    if (dist[end[i]] > dist[top.no] + weight[i]) {
                        dist[end[i]] = dist[top.no] + weight[i];
                        queue.add(new Item(end[i], dist[end[i]]));
                    }
                }
            }

            System.out.println(dist[n] == INF ? -1 : dist[n]);

        }
    }
}