就很普通……

import java.util.Arrays;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int N = 10010;
        int n = scanner.nextInt(), m = scanner.nextInt();
        int[][] g = new int[n + 1][n + 1];
        int[] distance = new int[n + 1];
        boolean[] state = new boolean[n + 1];

        // 初始化图和距离数组
        Arrays.fill(distance, N);
        distance[1] = 0;

        for (int[] i : g)
            Arrays.fill(i, N);
        while (m-- > 0) {
            int x = scanner.nextInt(), y = scanner.nextInt(), z = scanner.nextInt();
            g[x][y] = Math.min(g[x][y], z); // 题目中有重边，只要留下最小的
        }

        dijkstra(n, g, distance, state);

        if (distance[n] == N)
            System.out.println(-1);
        else
            System.out.println(distance[n]);
        scanner.close();
    }

    private static void dijkstra(int n, int[][] g, int[] distance, boolean[] state) {
        // 找起点到别的点的最短路径，共需要n-1次
        int m = n - 1;
        while (m-- > 0) {
            int indexOfMin = -1;
            for (int j = 1; j <= n; j++) {
                if (!state[j] && (indexOfMin == -1 || distance[j] < distance[indexOfMin])) {
                    indexOfMin = j;
                }
            }
            for (int j = 1; j <= n; j++) {
                distance[j] = Math.min(distance[j], distance[indexOfMin] + g[indexOfMin][j]);
            }
            state[indexOfMin] = true;
        }
    }

}