C++

#include <iostream>
#include <vector>
#include <queue>
using namespace std;

const int MAXSIZE = 150010;
const int INF = 0x3f3f3f3f;
int n, m;
vector<vector<pair<int, int> > > graph(MAXSIZE, vector<pair<int, int> >());
vector<bool> visited(MAXSIZE, false);
vector<int> dist(MAXSIZE, INF);
priority_queue<pair<int, int>, vector<pair<int, int> >, greater<pair<int, int> > > pq;

void addEdge(int from, int to, int weight) {
    graph[from].emplace_back(weight, to);
}

void dijkstra(int start) {
    dist[start] = 0;

    pq.emplace(dist[start], start);
    while (!pq.empty()) {
        auto [d, v] = pq.top();
        pq.pop();
        if (visited[v]) {
            continue;
        }

        visited[v] = true;
        for (const auto [w, u] : graph[v]) {
            if (!visited[u] && d + w < dist[u]) {
                dist[u] = d + w;
                pq.emplace(dist[u], u);
            }
        }
    }
}

void init() {
    int x, y, z;
    cin >> n >> m;
    while (m--) {
        cin >> x >> y >> z;
        addEdge(x, y, z);
    }
}

int main() {
    init();
    dijkstra(1);
    if (dist[n] == INF) {
        cout << -1 << endl;
    } else {
        cout << dist[n] << endl;
    }

    return 0;
}