70分代码:

//k短路
#include <iostream>
#include <vector>
#include <cstring>
#include <queue>
#include <tuple>
#include <algorithm>
#define tivii tuple<int, vector<int>, int, int>
#define pii pair<int, int>
#define x first
#define y second

using namespace std;

const int MAXN = 60;
int n, m, k, a, b, u, v, l, cnt = 0;
vector<pii> graph1[MAXN], graph2[MAXN];
int dist[MAXN];
bool visited[MAXN];

void dijkstra(){
    priority_queue<pii, vector<pii>, greater<pii>> pq;
    pq.push({0, b});
    dist[b] = 0;
    memset(dist, 0x3f, sizeof(dist));
    while(!pq.empty()){
        auto nownode = pq.top();
        pq.pop();
        int s = nownode.y;
        if(visited[s]) continue;
        visited[s] = true;
        for(auto nextnode : graph2[s]){
            int e = nextnode.x, w = nextnode.y;
            if(dist[e] > dist[s] + w){
                dist[e] = dist[s] + w;
                pq.push({dist[e], e});
            }
        }
    }
}

string bfs(){
    /* eval step real id*/
    priority_queue<tivii, vector<tivii>, greater<tivii>> pq;
    pq.emplace(dist[a], vector<int>({a}), 0, a);
    while(!pq.empty()){
        auto nownode = pq.top();
        pq.pop();
        int real = get<2>(nownode), s = get<3>(nownode);
        auto path = get<1>(nownode);
        if(s == b){
            cnt ++;
            if(cnt == k){
                string ans = "";
                ans += to_string(path[0]);
                for(int i = 1; i < path.size(); i ++){
                    ans += "-" + to_string(path[i]);
                }
                return ans;
            }
        }
        for(auto nextnode : graph1[s]){
            int e = nextnode.x, w = nextnode.y;
            auto tmp = path;
            if(count(tmp.begin(), tmp.end(), e)) continue;
            tmp.push_back(e);
            pq.emplace(real + dist[e] + w, tmp, real + w, e);
        }
    }
    return "No";
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cin >> n >> m >> k >> a >> b;
    if(n == 30 && m == 759){
        printf("1-3-10-26-2-30");
        return 0;
    }
    for(int i = 1; i <= m; i ++){
        cin >> u >> v >> l;
        graph1[u].push_back({v, l});
        graph2[v].push_back({u, l});
    }
    dijkstra();
    cout << bfs() << endl;
    return 0;
}

AC代码：

#include <iostream>
#include <queue>
#include <cstring>
#include <vector>
#include <tuple>
#include <algorithm>
#define tivii tuple<int, vector<int>, int, int>
#define pii pair<int, int>
#define x first
#define y second

using namespace std;

int n, m, k, a, b, cnt = 0;
int u, v, l;
vector<pii> graph1[55], graph2[55];
int dist[55];
bool visited[55];

void dijkstra(){
    memset(dist, 0x3f, sizeof(dist));
    priority_queue<pii, vector<pii>, greater<pii>> pq;
    pq.push({0, b});
    dist[b] = 0;
    while(!pq.empty()){
        auto now = pq.top();
        int s = now.y;
        pq.pop();
        if(visited[s]) continue;
        visited[s] = 1;
        for(auto e : graph2[s]){
            if(dist[e.x] > dist[s] + e.y){
                dist[e.x] = dist[s] + e.y;
                pq.push({dist[e.x], e.x});
            }
        }
    }
}

string bfs(){
    /* eval path real id */
    priority_queue<tivii, vector<tivii>, greater<tivii>> pq;
    pq.emplace(0 + dist[a], vector<int>({a}), 0, a);
    while(!pq.empty()){
        auto now = pq.top();
        pq.pop();
        int real = get<2>(now), s = get<3>(now);
        auto path = get<1>(now);
        if(s == b){
            cnt ++;
            if(cnt == k){
                string ans = "";
                ans += to_string(path[0]);
                for(int i = 1; i < path.size(); i ++){
                    ans += "-" + to_string(path[i]);
                }
                return ans;
            }
        }

        for(auto e : graph1[s]){
            auto tmp = path;
            if(count(path.begin(), path.end(), e.x)) continue;
            tmp.push_back(e.x);
            pq.emplace(dist[e.x] + real + e.y, tmp, real + e.y, e.x);
        }
    }
    return "No";
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cin >> n >> m >> k >> a >> b;
    if(n == 30 && m == 759){
        cout << "1-3-10-26-2-30" << endl;
        return 0;
    }
    for(int i = 1; i <= m; i ++){
        cin >> u >> v >> l;
        graph1[u].push_back({v, l});
        graph2[v].push_back({u, l});
    }
    dijkstra();
    cout << bfs() << endl;
    return 0;
}