AcWing 853. 有边数限制的最短路

#include <bits/stdc++.h>
using namespace std;
const int N=5e2+10,M=1e4+10;
int dist[N],backup[N];
int n,m,k;
struct Node{
    int a,b,w;
}nodes[M];
int bellman_ford(){
    memset(dist,0x3f,sizeof dist);
    dist[1]=0;
    for(int i=0;i<k;i++){
        memcpy(backup,dist,sizeof dist);
        for(int j=0;j<m;j++){
            int a=nodes[j].a,b=nodes[j].b,w=nodes[j].w;
            dist[b]=min(dist[b],backup[a]+w);
        }
    }
    if(dist[n]>0x3f3f3f/2) return -1;
        return dist[n];
}
int main(){
    cin>>n>>m>>k;
    for(int i=0;i<m;i++){
        int a,b,w;
        scanf("%d%d%d",&a,&b,&w);
        nodes[i]={a,b,w};
    }
    int t=bellman_ford();
    if(t==-1) printf("impossible");
    else printf("%d",t);
    return 0;
}