参考答案：

#include<iostream>
#include<cstring>

using namespace std;

const int N = 510;
int g[N][N];
int dis[N];
int n, m;
int st[N];

int dijkstra()
{
    memset(dis, 0x3f, sizeof dis);
    dis[1] = 0;

    for (int i = 1; i < n; ++i)
    {
        int t = -1;
        for (int j = 1; j <= n; ++j)
        {
            if (!st[j] && (t == -1 || dis[j] < dis[t]))
                t = j;
        }
        st[t] = 1;
        for (int j = 1; j <= n; ++j)
        {
            dis[j] = min(dis[j], dis[t] + g[t][j]);
        }
    }

    return dis[n];
}
int main()
{
    cin >> n >> m;

    memset(g, 0x3f, sizeof g);
    for (int i = 1; i <= m; ++i)
    {
        int x, y, z;
        cin >> x >> y >> z;
        g[x][y] = min(g[x][y], z);
    }

    if (dijkstra() == 0x3f3f3f3f) cout << "-1";
    else cout << dis[n];

    return 0;
}