有边数限制的最短路

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

const int N=10010,M=10010;
int n,m,k;
int dist[N];//存储距离
int back[N];//备份

struct Edge
{
    int a,b,w;
}edges[N];

int bellman_ford()
{
    memset(dist,0x3f,sizeof dist);
    dist[1]=0;
    for(int j=0;j<k;j++)//一共走了k步
    {
        memcpy(back,dist,sizeof dist);//先存储下来，用存下来的去放松
        for(int i=0;i<m;i++)//放松每条边
        {
            int a=edges[i].a,b=edges[i].b,w=edges[i].w;
            dist[b]=min(dist[b],w+back[a]);
        }
    }
    if (dist[n]>0x3f3f3f3f/2)return -1;
    return dist[n];

}

int main()
{
    cin>>n>>m>>k;
    for(int i=0;i<m;i++)
    {
        int a,b,w;
        cin>>a>>b>>w;
        edges[i]={a,b,w};
    }
    int t=bellman_ford();

    if(t==-1)puts("impossible");
    else printf("%d\n",t);
    return 0;
}