AcWing 850. Dijkstra求最短路 II 堆优化版 优先队列 稀疏图

//稀疏图 点和边差不多
#include <cstring>
#include <iostream>
#include <algorithm>
#include <queue>
using namespace std;
typedef pair<int, int> PII;
const int N = 1e5 + ;
int n, m;
int h[N], e[N], ne[N], idx;
int w[N];//表示权值
int dist[N];
bool st[N];
void add(int a, int b, int c) {
    e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx ++ ;
}
int dijkstra() {
    memset(dist, 0x3f, sizeof dist);
    dist[] = ;
    priority_queue<PII, vector<PII>, greater<PII>> heap;//小根堆
    heap.push({, });//起点到起点的距离为0
    while (heap.size()) {
        auto t = heap.top();//找到距离最小的点
        heap.pop();//删掉
        int ver = t.second, distance = t.first;
        if (st[ver]) continue;//如果这个点之前已经出来过，就跳过
        st[ver] = true;//
        for (int i = h[ver]; i != -; i = ne[i]) {//遍历所有临边
            int j = e[i];
            if (dist[j] > distance + w[i]) {
                dist[j] = distance + w[i];
                heap.push({dist[j], j});
            }
        }
    }
    if (dist[n] == 0x3f3f3f3f) return -;
    return dist[n];
}
int main() {
    scanf("%d%d", &n, &m);
    memset(h, -, sizeof h);
    while (m -- ) {
        int a, b, c;
        scanf("%d%d%d", &a, &b, &c);
        add(a, b, c);
    }
    cout << dijkstra() << endl;
    return ;
}