acwing853. 有边数限制的最短路

#include<iostream>
#include<cstring>
using namespace std;

const int N=510,M=10010;

int n,m,k;
int dist[N],last[N];
struct Edge{
    int a,b,c;
    
}edges[M];
void bellman_ford(){
    memset(dist,0x3f,sizeof dist);
    dist[1]=0;
    for(int i=0;i<k;i++){
        memcpy(last,dist,sizeof dist);
        for(int j=0;j<m;j++){
            auto t=edges[j];
            dist[t.b]=min(dist[t.b],last[t.a]+t.c);
        }
    }
}


int main(){
    cin>>n>>m>>k;
    for(int i=0;i<m;i++){
        int a,b,c;
        cin>>a>>b>>c;
        edges[i]={a,b,c};
    }
    bellman_ford();
    if(dist[n]>0x3f3f3f3f/2)puts("impossible");
    else cout<<dist[n]<<endl;;
    
    return 0;
}