0魔法阵 - 蓝桥云课 (lanqiao.cn)

#include <iostream>
#include <queue>
#include <vector>
#include <cstring>
#include <algorithm>

using namespace std;

#define x first
#define y second
const int N = 1010;
const int inf  = 1e4;
vector<pair<int,int>> a[N];
int f[N][20];
int st[N];

int main(){
    int n,k,m;
    cin>>n>>k>>m;
    int u,v,w;
    while(m--){
        cin>>u>>v>>w;
        a[u].push_back({v,w});
        a[v].push_back({u,w});
    }
    queue<int> q;
    memset(f,inf,sizeof f);
    f[0][0] = 0;
    q.push(0);

    while(q.size()){
        int u = q.front();
        q.pop();
        st[u] = 0;
        for(auto i : a[u]){
            int v = i.first;
            int w = i.second;
            bool flag = false;
            if(f[v][0]>f[u][0]+w){
                f[v][0] = f[u][0]+w;
                flag = true;
            }
            for(int i = 1;i<=k;i++){
                if(f[v][i]>f[u][i-1]){
                    f[v][i] = f[u][i-1];
                    flag = true;
                }
            }
            if(f[v][k]>f[u][k]+w){
                flag  = true;
                f[v][k] = f[u][k]+w;
            }
            if(flag&&!st[v]){
                q.push(v);
                st[v] = 1;
            }

        }
    }

    cout<<min(f[n-1][k],f[n-1][0]);

    return 0;
}