参考答案：

#include<iostream>
#include<queue>
#include<vector>
#include<cstring>

using namespace std;

const int N = 200010;
typedef pair<int, int> PII;
int e[N], ne[N], h[N], w[N], idx;
int st[N];
int n, m;
int dis[N];

void add(int a, int b, int c)
{
    w[idx] = c, e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}

int dijkstra()
{
    memset(dis, 0x3f, sizeof(dis));
    dis[1] = 0;
    priority_queue<PII, vector<PII>, greater<PII>> heap;
    heap.push({ 0,1 });

    while (heap.size())
    {
        auto t = heap.top();
        heap.pop();
        int ver = t.second;
        if (st[ver]) continue;
        st[ver] = true;
        for (int i = h[ver]; i != -1; i = ne[i])
        {
            int j = e[i];
            if (dis[j] > dis[ver] + w[i])
            {
                dis[j] = dis[ver] + w[i];
                heap.push({ dis[j],j });
            }
        }
    }

    if (dis[n] == 0x3f3f3f3f) return -1;
    else return dis[n];
}
int main()
{
    memset(h, -1, sizeof(h));
    cin >> n >> m;

    for (int i = 1; i <= m; ++i)
    {
        int a, b, c;
        cin >> a >> b >> c;
        add(a, b, c);
    }

    cout << dijkstra() << endl;

    return 0;
}