C++代码

#include<iostream>
#include<algorithm>
#include<cstring>

using namespace std;

const int N=510,M=10010;

int n,m,k;
int dist[N],backup[N];

struct Edge 
{
    int a,b,w;
}edge[M];

int bellman_ford()
{
    memset(dist,0x3f,sizeof dist);
    dist[1]=0;

    for(int i=0;i<k;i++)
    {
        memcpy(backup,dist,sizeof dist);    //备份，防止串联 
        for(int i=0;i<m;i++)
        {
            int a=edge[i].a,b=edge[i].b,w=edge[i].w;
            dist[b]=min(dist[b],backup[a]+w);
        }
    }

    if(dist[n]>(0x3f3f3f3f/2)) return -1;
    return dist[n];
}//bellman_ford

int main(void)
{
    scanf("%d%d%d",&n,&m,&k);

    for(int i=0;i<m;i++)
    {
        int a,b,w;
        scanf("%d%d%d",&a,&b,&w);
        edge[i]={a,b,w};
    }

    int res=bellman_ford();

    if(res==-1) puts("impossible");
    else printf("%d\n",res);

    return 0;
}