如果搜索到距离更近的点，就要更新这一点的距离，但是不一定需要将其放入优先队列中，因此需要一个判重数组st，检测该点是否是最近的点。

未优化版：

#include <iostream>
#include <cstring>
#include <queue>
using namespace std;
typedef pair<int, int> PII;

const int N = 150010, INF = 0x3f3f3f3f;
int e[N], ne[N], w[N], h[N], idx;
int d[N];

void add(int x, int y, int z) {
    e[idx] = y;
    ne[idx] = h[x];
    w[idx] = z;
    h[x] = idx;
    idx++;
}

void dijkstra() {
    memset(d, 0x3f, sizeof d);
    d[1] = 0;
    priority_queue<PII> heap;
    heap.push({ 0, 1 });

    while (heap.size()) {
        PII t = heap.top();
        heap.pop();

        int dist = t.first, ver = t.second;

        for (int i = h[ver]; i != -1; i = ne[i]) {
            if (d[e[i]] > dist + w[i]) {
                d[e[i]] = dist + w[i];
                heap.push({ d[e[i]], e[i] });
            }
        }
    }

}

int main() {
    memset(h, -1, sizeof h);
    int n, m;
    cin >> n >> m;
    for (int i = 0; i < m; i++) {
        int x, y, z;
        cin >> x >> y >> z;
        add(x, y, z);
    }

    dijkstra();

    if (d[n] == INF) {
        cout << -1;
    }
    else {
        cout << d[n];
    }
    return 0;
}

优化版：

#include <iostream>
#include <cstring>
#include <queue>
using namespace std;
typedef pair<int, int> PII;

const int N = 150010, INF = 0x3f3f3f3f;
int e[N], ne[N], w[N], h[N], idx;
int d[N];
bool st[N];

void add(int x, int y, int z) {
    e[idx] = y;
    ne[idx] = h[x];
    w[idx] = z;
    h[x] = idx;
    idx++;
}

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

    while (heap.size()) {
        PII t = heap.top();
        heap.pop();

        int dist = t.first, ver = t.second;

        if (st[ver]) {
            continue;
        }
        st[ver] = true;

        for (int i = h[ver]; i != -1; i = ne[i]) {
            if (d[e[i]] > dist + w[i]) {
                d[e[i]] = dist + w[i];
                if (!st[e[i]]) {
                    heap.push({ d[e[i]], e[i] });
                }
            }
        }
    }

}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    memset(h, -1, sizeof h);
    int n, m;
    cin >> n >> m;
    for (int i = 0; i < m; i++) {
        int x, y, z;
        cin >> x >> y >> z;
        add(x, y, z);
    }

    dijkstra();

    if (d[n] == INF) {
        cout << -1;
    }
    else {
        cout << d[n];
    }
    return 0;
}