飞行路线
实际上就是建立k + 1层图

#include<iostream>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;
const int N = 110010, M = 2500010; 
int n, m, k, s, t;
int tot;
priority_queue<pair<int, int>> q;


int h[N], e[M], ne[M], dist[N], idx, w[M];
bool st[N];

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

void dijkstra(int s){
    memset(dist, 0x3f, sizeof dist);
    dist[s] = 0;
    q.push({0, s});
    while(q.size()){
        int x = q.top().second;
        q.pop();
        if(st[x]) continue;
        st[x] = true;
        for(int i = h[x]; i != -1; i = ne[i]){
            int j = e[i];
            if(dist[j] > dist[x] + w[i]){
                dist[j] = dist[x] + w[i];
                q.push({-dist[j], j});
            }
        }
    }
}

int main(){
    scanf("%d%d%d", &n, &m, &k);
    scanf("%d%d", &s, &t);
    memset(h, -1, sizeof h);
    for(int i = 0, a, b, c; i < m; i ++ ){
        scanf("%d%d%d", &a, &b, &c);
        add(a, b, c), add(b, a, c);
        for(int j = 1; j <= k ; j ++ ){
            add(a + (j - 1) * n, b + j * n, 0);
            add(b + (j - 1) * n, a + j * n, 0);
            add(a + j * n, b + j * n, c);
            add(b + j * n, a + j * n, c);
        }
    }

    for(int i = 1; i <= k; i ++ ){
        add(t + (i - 1) * n, t + i * n, 0);
    }

    dijkstra(s);

    printf("%d\n", dist[t + n * k]);

    return 0;
}